To date, there are a lot of cases of fire in the premises. Due to the fact that modern technology does not stand still, currently there are various ways to protect against sudden fire. Few people pay attention to such a small hidden device as a fire detector. Usually they are installed on the ceilings of offices and apartments. These products are even specially designed in such a way as to blend in with the decor and fit well into any interior. But on these simple and inconspicuous devices depends on the lives of people and the safety of property.
Device description
What is a fire alarm sensor? Let's dwell on this in more detail. In fact, calling it a sensor is not entirely correct, since it is considered only an element that responds to thermal, light, chemical or other effects. In addition to the sensor itself , the fire detector includes other elements. The device depends on the specific model. It may include signal recognition elements, an information exchange system, a re-inclusion design, and other components.
Classification
There are a huge number of fire detectors of various types and types. They can be classified according to various criteria:
1. According to the principle of the issued signal: the transmission system is a mandatory structural element that is present in absolutely all fire detectors. The existence of the device itself without such a system would be meaningless.
The following devices are distinguished:
- Single-mode detectors: generate and transmit a fire signal with a sufficiently long exposure to an external factor, which is designed to monitor the fire sensor. Typically, such devices are triggered by high temperatures. Single-mode devices are currently practically not used.
- Two-mode detectors: form and transmit two signals at once - “Fire” and “No fire”. It may seem to some that the signal that there is no fire is unnecessary, because the Fire signal indicates a hazardous environment. However, everything is not so simple. The “No fire” signal indicates that the detector is in good condition and is monitoring the situation in real time. A malfunction of a single-mode fire detector can only be found out during the verification process. Every day no one will arrange such checks. For this reason, dual-mode devices are more popular than single-mode devices.
- Multi-mode devices: A feature of this type of sensor is that it reports a malfunction with a special type of signal. However, this does not mean that the detector is completely out of order. This quality is especially useful, even irreplaceable, at large facilities where it will take time to find a faulty detector. Having determined the nature of the malfunction, the master will be able to eliminate it. The multi-mode device is also capable of generating other signals, for example, “sensor contamination”.
2. By type of signal transmission:
- Wired: the signal in such detectors is transmitted via cable.
- Wireless: use a radio signal or a mobile communication channel to transmit a signal.
3. By type of parameter change:
- Differential: they give a reaction not to the absolute value of the checked parameter, but to its dynamics.
- Threshold devices: register when the parameter monitored by the sensor reaches a critical value, after which an alarm is triggered.
- Combined devices respond to both types of parameter changes.
4. By localization:
- Spot: have one sensor assembled with the detector. Such devices are most often used in everyday life.
- Multipoint detectors: they have several sensors at once.
- Linear: control the space along an arbitrary line. They are paired and single.
Fire detectors also differ in type of sensor. This type of classification should be considered in more detail.
Thermal Sensors
What is their feature? These heat detectors appeared long ago and for a long time remained the most common. The first fire safety devices , which appeared back in the 19th century, were a pair of spring-loaded wires separated by a wax insert. With increasing temperature, the wax melted, the wires connected and closed the circuit, thereby triggering an alarm.
Modern fire safety sensors typically contain fusible elements. Other triggering principles may also be used, such as the thermoelectric effect. It occurs at a certain temperature at the junction of two different conductors (thermocouple). The most common sensors that were installed in Soviet high-rise buildings are based on this principle.
With all the advantages of thermal sensors, they have one significant minus: the air temperature rises significantly only when the flame has already ignited. Therefore, gradually such devices are losing ground.
Smoke alarms
What are they and what is their feature? Fire smoke detectors today confidently lead in alarm systems installed in office and residential buildings. After all, the first sign of a starting fire is smoke. It may appear even before a fire occurs. For example, wiring under conditions of low oxygen levels for a long time may be at the stage of decay.
How do fire alarms (smoke alarms) work? The principle of operation is based on a change in the transparency of smoky air. Linear detectors emit a directional beam of light in the optical or ultraviolet range. A beam of light in conditions of normal transparency freely passes the intended segment of the monitored space and enters the reflector. If smoke closes the path to the beam, then the photocell will fix this and the detector will emit a signal.
A point emitter emits into the space beams of infrared radiation scattered by air, which is completely transparent in the optical spectrum. However, for a range, it is not. A low-intensity infrared beam will simply not be able to reach the nearest obstacle and bounce to the detector. It is important to observe the minimum distances from the sensor to the obstacle when connecting the detectors. Smoke emitted during smoldering reflects infrared rays well. The beam is reflected from the smoky area, which leads to the fire protection.
The fire alarm point sensor has a simple device and is relatively inexpensive. However, they also have their drawbacks. Such sensors are not too reliable. For example, dense black smoke does not reflect, but absorbs infrared rays. Therefore, when burning rubber and diesel fuel, such detectors may be ineffective.
Flame sensors
What are they? A fire sensor that responds to a flame is usually installed in industries where it is impossible to use heat and smoke emitters due to a specific nature: increased air temperature, smoke or dustiness of the air.
By the principle of operation, flame sensors can be infrared. Such devices capture radiant heat from a flame. In a room where infrared sources, such as heaters, constantly work, it is better to use ultraviolet flame sensors. There are also devices that respond to the electromagnetic component of open flame radiation. Such a sensor is able to detect fire even at a great distance.
Security ultrasonic motion sensors can very well be used as fire detectors. The principle of their action is based on the recognition of the nature of the propagation of ultrasound in still and moving air. The flow of air masses can be caused not only by the actions of the intruder, but also by fire. For this reason, ultrasonic sensors may well indicate the onset of a fire.
Now that you know about the main varieties of fire detectors and the principle of their operation, you can begin to consider the rules for their installation.
Fire Alarm Installation
Let's dwell on this aspect in more detail. How to install fire sensors in the apartment? In order for the device to respond to the fire properly, it is necessary to take into account a lot of features. The main ones are listed below:
- It is best to mount the fire detector on the ceiling. If the design makes installation difficult, it is possible to fix them on tension ropes or columns, at a distance of no more than 30 cm from the ceiling.
- One electric circuit can combine no more than 10 devices for administrative premises and residential apartments and no more than 5 devices in production. When using an addressable connection scheme, the number of devices in one loop can reach 20.
- If there are objects in the room whose upper edge is less than 60 cm from the ceiling, it is imperative to place the detector in each of the zones formed by such objects.
- The area controlled by the device must correspond to the values given in the technical data sheet of a particular model.
How to choose a fire alarm?
This aspect should be given special attention. Today, many people want to have fire detectors at home. Systems of this kind can differ in many ways. The cost of the detector should not be a decisive criterion for selection. For installation in urban apartments, it is better to use addressable devices. The complex architecture of the room makes it difficult to use autonomous systems. When using addressable detectors, it is better to connect to the control device according to the radial scheme. If the cable wires are hidden behind false walls or a false ceiling, then the space between the ceiling and the lining must be in the control zone of detectors connected to a separate cable.
Installation of fire sensors should be carried out in such a way that in case of a malfunction they can easily be removed from the wall and replaced.
Mounting
So what is its feature? Fire smoke detectors are installed in accordance with the plan and wiring diagram. Installation of such systems is best provided to specialists. Connecting sensors can be triangular or square. When installing, it is important to consider the distance between the opposite walls, as well as between the sensors. For example, if the height of the room is less than 8 meters, the distance between the thermal sensors should be 7 meters when using the square arrangement and 8.6 meters in the triangular arrangement. The distance between the sensor and the wall should be 3.5 and 2.5 meters, respectively. If the height of the room is from 8 to 11 meters, these schemes can only be used in individual cases.
Fire smoke detectors can be installed in a square or triangular arrangement only in case of a large room height. If it reaches 11 meters, the distance between the sensors using a square scheme should be 10.5 meters, and when using a triangular, 13 meters. The distance between the wall and the sensor is 5.3 and 3.75 m, respectively.
How should the sensors be installed? The fire system can be organized in three ways:
- Address: allows you to accurately identify the place of ignition.
- Address-analog: provides the ability to achieve a better reaction rate in case of fire.
- Threshold: used only in small areas.
Connection
Let's take a closer look at this. What do you need to connect a fire alarm sensor? The main elements of such systems are the power supply, control device, display unit, alarm control equipment and the sensors themselves. Nevertheless, it is not always possible to establish such classical systems. There are many objects on which it is impossible to carry out installation of complex alarms. However, fire detection systems on them are still necessary for fire safety. To solve this problem, autonomous fire detectors can be used. Such systems are connected to stand-alone power devices and can be removed from stationary loops of warning systems.
The simplest example of this design is a battery-powered fire detector. It can be installed both alone and within a single system. One device allows you to organize a fire protection system in a room with an area of up to 50 square meters. The alarm turns on as soon as smoke is in the air chamber. At the same time, a sound and light signal appears. The system is powered by batteries up to 9 V.
Key device options
Let's dwell on them in more detail. If you want to install fire sensors in the apartment, you need to pay attention to the following device parameters:
- reaction rate to fire;
- energy costs necessary for the operation of the system;
- sensitivity of elements;
- the ability to configure the trap;
- method of mounting the sensor;
- operational safety;
- system maintenance method;
- compliance with the height and area of the room;
- the possibility of using autonomous power sources.
Conclusion
Today in residential and administrative buildings a fire detector must be installed. This is the simplest security measure one day can save your life. In new homes and apartments, such systems are usually planned at the design stage. If your home is not equipped with fire detectors, you can install them yourself.