It is impossible to be prepared for a fire, it is always sudden and uncontrollable. But it is possible to minimize the risk of its occurrence by significantly reducing the predictable material damage. To do this, specialists invented fire detectors, which are currently the only means capable of detecting a fire without a person. One of these of its kind is a thermal fire detector or detector, briefly — TPI.
The principle of operation of TPI and features of its design
The name itself — thermal — explains the principle of operation of the device. It contains one or more transducers — sensitive elements, which, perceiving the temperature increase in the environment, lead to the operation of a loud identification signal through an audible annunciator.
There is another type of detector — fire smoke. It is triggered by aerosol combustion products, in other words, smoke, or rather, its color. The advantage of fire smoke detectors is that it is allowed in administrative buildings, unlike a heat detector, and the minus is that it will raise everyone to their feet not because of a fire, but, for example, a large accumulation of dust or steam. Moreover, strictly speaking, it is wrong to call it a sensor, because it is only an integral part of the detector.
By the appearance of the main component of the TPI — a sensitive element or controller, there are four main types of it:
- Contact TPI. When the temperature regime changes, the established contact or the electrical circuit opens, the special loop breaks and causes the sound signal to sound. The simplest, as a rule, domestic models, are a closed contact of two conductors, packed in a plastic container. More complex ones have a temperature-sensitive semiconductor with negative resistance. If the temperature mark of the environment increases, the resistance will drop, and a controlled current will flow through the circuit. As soon as it reaches a certain indicator, the alarm will work.
- AT electronic sensor mounted sensors that are inside the cable, as soon as the temperature reaches a certain threshold, the resistance of the electric current in the cable changes, which is transferred to the control of the control device. Highly sensitive. The principle of the device is quite complicated.
- Optical detector works on the basis of an optical fiber cable. As the temperature rises, the optical conductivity changes, which leads to an audible warning.
- Metal tube with gas, hermetically filled, required for mechanical TPI. The impact of temperature on any part of the tube will lead to a change in its internal pressure and an alarm will be triggered. Declared obsolete.
- Other types. Semiconductor ones have a special coating with a negative temperature coefficient, electromechanical ones consist of wires under mechanical stress coated with a temperature-sensitive substance.
Types of fire detectors
Thermal firefighters react to different parameters of the spread of fire. Hence the classification into types.
The absolute value threshold is set to the maximum fire detector:
- temperature — as soon as the environmental indicator reaches it, people will be notified.
Domestic devices are mass-produced with a response temperature of 70–72 degrees. They are also very popular because of their affordability.
For a differential fire alarm sensor, the rate of change of the attribute that it controls is important.
Such devices are recognized as more efficient than the maximum TPI -
- give early warning
- stable in operation, but due to two elements installed at a distance, they are more expensive.
Maximum differential instruments combine both parameters.
If you are going to purchase this type of fire equipment, please note that their temperature threshold must be at least 20 degrees higher than the permitted temperature at the facility.
Thus, technical specialists divide modern fire alarm systems into discrete (by threshold) — they are discussed above — and analog. Analog thermal fire sensors, in turn, are divided into conventional and addressable. The latter transmit not only information about the fire, but also the code of their address.
Both discrete and analog measure the characteristics of fire factors, the fundamental difference is in the way the signal is processed.
For analog ones, it is more complicated and its essence is in special systematic algorithms.
- Addressable analog thermal devices regularly collect information about the state of the premises. They can give out the data they are programmed to collect in real time.
- Explosion-proof thermal fire detectors are needed where the risk of fire is high and explosive substances may be present in the air. They seem to be armored, as they are located on various power units, oil pipelines, etc. They differ in the degree of protection, the number of sensors and the different temperature thresholds set.
- At linear heat detectors a cable with a heat-sensitive polymer is used — a thermal cable — it captures any changes along its entire length as a single fire sensor. Used where the ceiling is large, such as an indoor stadium. You can also mount on the walls in addition to the ceiling.
- Multi-point thermal devices opposed to inherently linear. They are part of a single system that controls several zones and is combined into an electrical circuit. The signals coming from fire sensors are processed in a single unit.
Operation and installation
The connection diagram for thermal sensors is given in the instruction manual, however, difficulties may arise.
The requirements of GOST R 53325–2009, paragraph 126.96.36.199, oblige to supply heat detectors with a built-in or remote optical indicator.
When calculating the values of additional resistors, take into account the electrical components of the connected LED indicators.
Look in the device data sheet for the typical and maximum voltage drop, which indicate the limit of the parameters. For ease of installation, it is better to take LED non-polar indicators.
Normally closed contacts of thermal devices are connected to the loop in the same way as for smoke devices. The difference is that in the standby state, thermal sensors do not consume electric current, and in active mode it is less than that of smoke sensors.
Thermal fire alarm sensors have the following resistances in the connection diagram:
We study the instruction manual for the control device and take into account the resistor values.
Rbal. similar to Radd., but it is not included in the control device kit, you will have to buy it additionally.
In normal mode, the sensors are short-circuited, which means that the resistance Rbal will occur only if one or two of the devices work. And then the “Alarm” signal can be formed.
For controllersMirage” is the following diagram. If one works, then the “Attention” signal will come in, if the second one, the “Fire” command will follow.
The designation of the heat detector in the diagram, as well as other components, is as follows:
- ShS — alarm loop
- IP — thermal fire detector,
- YPRES — manual fire detector
- DIP — fire smoke detector.
Conditional graphic designation of an automatic heat detector according to the requirements of regulatory documentation — .
Norms and features of installation / connection of thermal sensors are regulated withwater of the rules of the fire protection system 188.8.131.529 with the latest changes from 20.06.2011
From table 13.5, the distance between the thermal spot devices, as well as between them and the wall, becomes known (do not forget about the exceptions indicated in paragraph 13.3.7).
It is easy to guess that the area covered by the sensor depends on the height of the room. At the same time, many install two devices in each room in case one sensor fails.
The distance from one to the other should be limited to half the recommended. But this works with point non-address sensors. Analog addressable ones do not need duplication, since they have a completely different principle of operation.
- When locating sensors in rooms, it is necessary to take into account the peculiarities of the distribution of combustion products in them.
- It is inefficient to install heat sensors in “dead” zones, where the hot air will reach the last place, and the fire extinguisher will work too late.
- So, when laying a thermal cable of a linear heat detector, it is not necessary to do this 15–20 cm from the corners along the ceiling and walls.
- Do not forget about hoods, air conditioners — place the device at least a meter away from them.
Physical laws give rise to the principles that underlie the installation of fire detectors:
- a flat ceiling is protected along a circle lying in a horizontal surface;
- you need to take into account the distance from the ceilings of the room.
Faults and solutions
First of all, we read about them in the instruction manual in a specially dedicated section. The description indicates what may not work and what method will help fix the problem.
The classic reasons are unprofessional installation and factory defects. A detected marriage leads to a warranty period, which averages from 18 to 36 months, but sometimes 12 months.
- Experienced engineers also point out a false fire alarm in the event of a repair, when dust gets into the device and it goes off.
- Sometimes insects also serve as a cause for unjustified anxiety. Rubbing with alcohol and blowing helps.
- Loops can periodically notify of a fire with twisted wires, where the contact is unstable.
- No one has canceled electromagnetic interference from devices, so they must be taken into account. Seasonal changes, acoustic fluctuations and aggressive environments also affect malfunctions.
- False alarms often do not indicate the high sensitivity of the detectors, but low quality. Experts also warn that all cheap developments lose their level of sensitivity over time. And here only a replacement will help.
To solve most problems with a malfunction, checking the connections, the correct location of the detectors and the normal operation of the contact connections will help.
Also, high-quality components of the detectors will help to prevent the non-detection of a fire.
Manufacturers and popular models
Fire detectors are produced by European and foreign manufacturers. Among them
- oldest Japanese company Hochiki,
- most popular Siemenswhich was joined by the Swiss manufacturer Cerberus.
- Fire detectors from a British company have proven themselves well Appolo.
- Also well known System Sensorwhose products are produced in 8 largest countries — from the USA to Europe.
In our country, specializes in fire heat detectors
- company “Argus-Spectrum“located on the basis of the scientific and industrial complex in the world.
- Kitstroyservis is one of the leaders in domestic developments.
- Magneto-Contact produces sensors based on sealed contacts,
- a wide range of products fromSiberian Arsenal”,
- research and production enterprise “Spetsinformatika-SI”.
- Also, private enterprise offers its products “Arton” and “Spetsavtomatika”.
The simplest maximum fire-fighting thermal appliances are domestic, their price is from 40 rubles to 150.
- Additional options, for example, a memory for a triggered device, a light and / or remote indicator, an increase in their number entails a doubling in price, a spread of 270 rubles. and up to 600.
- Maximum differential sensors can be purchased for a price of 5 dollars. up to 900.
- One of the best selling models Aurora TN (IP 101–78-A1)its price is an average of 7 dollars.
- The most popular explosion-proof detector model due to its affordability IP 101–3A-A3R will cost 2 dollars on average, although most stores offer explosion-proof devices from 800 to 10 dollars.
Foreign addressable maximum differential devices
- cost from 10 dollars per piece and higher.
- Among the address-analog maximum-differential — bestseller model S2000 IP-03She is standing from 500 to 8 dollarsbut in general, the run-up of addressable detectors reaches 2,000 and even higher.
- thermal sensors — thermal cables — depending on the characteristics (cable resistance, maximum allowable length, current voltage, etc.), they are sold on average from 300 to 7 dollars.
Information about the principles of operation, design features, types and types of thermal fire detectors will help you choose the most suitable model in a balanced way and without unnecessary financial costs. Installation rules and regulations are not that complicated, and if you take them responsibly, you can prevent many malfunctions. And it is best to carry out the installation under the strict guidance of experienced electricians.