It is better to prevent a fire in advance than to fight the raging fire elements later. Since a fire may not always be accompanied by smoke, it would be a mistake to use exclusively smoke detectors in an automatic system. They are always paired with heat sensors that duplicate the smoke alarm, which ensures that the signal reaches the remote control in any case.
Thermal fire detectors or thermal sensors are designed to detect sources of ignition within their range and generate an alarm signal. The principle of operation of the simplest can be imagined as an electrical circuit broken by the contacts of a thermal relay.
If a fire occurs, the contacts close under the influence of high temperature and thereby supply current to the duty control panel.
Current systems with heat detectors have become noticeably more complex, but the failure factor has also decreased significantly. The sensors are always placed on the ceiling, above places of possible fire, since it is at the top that the hot air concentrates.
Unlike devices where the triggering factor depends on the color of the smoke, its components or the purity of the air in the room, thermal sensors always respond only to a set temperature threshold starting from 50 ° C and are undemanding to the level of dust content.
Despite the fact that the triggering criterion is high temperature, characterized by stable characteristics, detectors of different operating principles can be used to build a sensor system, which is determined by external factors.
Installation of linear temperature sensors in rooms with a large area should only be done in pairs with a thermal cable. Otherwise, even the most efficient fiber optic models will become practically useless, since it will be impossible to determine the exact location of the trigger. This rule can be ignored for small low-rise buildings and often they use ordinary twisted pair or even telephone cable.
If the premises do not have a climate control system, then with a significant increase in air temperature false alarms often occur, therefore, at this time of the year, measures should be taken to promptly check the equipment at the installation site in the event of an alarm.
There is a microcontroller installed inside the detector, installed in a remote temperature-sensitive unit that has a protected casing. The remote unit is connected to an explosion-proof terminal box made of brass; inside the box there is a relay, which, when a signal about an increase in temperature is received, opens the contacts, thereby breaking the circuit and sending a signal to the control panel.
The detector is of the same importance as the smoke detector, therefore, specialists of the appropriate profile must be involved to create a multi-stage circuit. When constructing simple circuits, a distinction should be made between explosion-proof and other models. The former have a higher cost due to the metal body, and are intended only for industrial premises.
For premises such as warehouses, it is suitable to use a thermal cable with the connection of point detectors to it. In other cases, and especially when installed in rooms with a high risk of fire, such as libraries, server rooms, and public spaces decorated with fire-hazardous materials, linear or differential models can be used, both with a thermal cable and with a regular line.
Thermal fire detector is an automatic PI that responds to a certain temperature value and (or) the rate of its increase (GOST R53325-2012).
When equipping facilities with automatic fire alarm systems, three types of thermal fire detectors are widely used: with sensors of maximum, differential and maximum-differential action
Classification of thermal PIs according to the nature of the reaction to a controlled sign of fire:
Maximum thermal fire detector- a fire detector that generates a fire notification when the ambient temperature exceeds the established threshold value - the detector response temperature.
Maximum differential thermal fire detector- a fire detector that combines the functions of maximum and differential thermal fire detectors.
Differential thermal fire detector- a fire detector that generates a fire notification when the rate of increase in ambient temperature exceeds the established threshold value.
Detectors with maximum action sensors are triggered at a certain, preset temperature.
Detectors with differential sensors respond to a certain rate of temperature increase.
Maximum-differential detectors include maximum and differential action sensors and are triggered both at a certain, predetermined temperature and at a certain rate of its increase.
When choosing thermal fire detectors, it should be taken into account that the response temperature of maximum and maximum differential detectors must be at least 200 C higher than the maximum permissible air temperature in the room.
Thermal fire detectors are classified depending on the sensing element used.
Fusible sensor detectors are considered the most common due to their simplicity, reliability and low cost. Being a one-time action, they cannot serve as information about the restoration of normal conditions in controlled premises.
Currently, detectors using thermocouples as sensors are widely used. The thermocouple differential detector contains a thermopile, which provides a fire signal when there are signs of an increase in the ambient temperature above the maximum permissible. The faster the temperature rises, the sooner the fire danger signal is given.
Classification of thermal PIs according to the operating principle:
IP101 - using the dependence of the change in the value of thermal resistance on the temperature of the controlled environment;
IP-102 - using thermoEMF generated during heating;
IP-103 - using linear expansion of bodies;
IP-104 - using fusible materials;
IP-105 – using the dependence of magnetic induction on temperature;
Classification according to the configuration of the measuring zone: thermal PIs are:
A point fire detector is a fire detector that responds to fire factors in a compact area.
Multipoint fire detector (thermal) – a detector with a discrete arrangement of point sensitive elements in the measuring line.
Linear fire detector - a fire detector that responds to fire factors in an extended, linear zone.
For example:
Point thermal detector maximum 70°C IP-103-4/1 MAK-1
Device: The detector consists of a plastic protective housing and a plastic base with two mounting holes for screws, in which a temperature relay is installed directly on the screw terminals. A shunt resistor is mounted to the same terminals.
Operating principle: In normal condition, the contact system of the detector is closed. When the threshold temperature is reached, the detector contacts open, and when the temperature drops from the threshold, the contacts close again.
Multipoint thermal detector IP 102-2x2
The detector sensor consists of sensing elements (thermocouples) evenly distributed on a long twisted wire.
Principle of operation: Thermal emfs that arise when thermocouples are exposed to heat flows are summed up at the ends of the wire and converted in a special electronic unit (interface unit) into an alarm signal. If a wire with thermocouples is evenly placed over the entire ceiling area of the protected room, then by scanning the heat flows in the room, fires are quickly detected. The results of fire tests showed that the response time of multipoint detectors depends little on the height of the protected premises and amounts to several tens of seconds up to a height of H = 20 m.
Linear heat detector (thermal cable)
Thermal cable device:
A linear detector (thermal cable) consists of two steel conductors, each of which is coated with thermoplastic material. The conductors are twisted together to create mechanical tension between them, and are additionally covered with an outer protective PVC sheath.
Principle of operation:
The control current from the interface module constantly passes through the thermal cable. At the actuation temperature, the thermoplastic insulation material is pressed through due to the mechanical stress of the conductors, and they short-circuit. The thermal cable works as a single continuous sensor. Linear detection has unique advantages when used in places with difficult access, places with increased pollution, dust, aggressive or explosive environments.
Scope of thermal PIs
Thermal PIs are used to protect premises whose flammable load is characterized by significant heat release during a fire. If the control zone is an extended object of complex geometric shape, linear TPIs are used.
Maximum TPI should not be used in rooms where the air temperature may be below 0ºС and in rooms intended for storing cultural property, for containing flammable materials in small quantities and/or with low calorific value.
Differential TPIs are effectively used to protect objects with low ambient temperatures. The inertia of differential detectors is lower than that of maximum detectors, which means that a fire will be detected faster. At the same time, differential TPIs should not be used to protect premises in which significant temperature changes are possible, not caused by a fire, but associated, for example, with the operation of air conditioning systems.
The appearance of fires is characterized by an increase in ambient temperature. Therefore, heat detectors are most often used in fire alarm systems.
They are able to identify fires at the initial stage, which allows timely measures to be taken to eliminate them. However, such sensors are presented in various modifications on the market.
To choose the right one for a specific room, you should learn as much as possible about them.
What is a detector? This is a heat-sensitive element enclosed in a plastic case. The operating principle of the simplest models is based on closing/opening contacts, leading to the formation of a signal.
For the device to operate, the ambient temperature must rise above the device’s threshold value.
When operating, such heat detectors do not consume current. They are called passive. They use a specific alloy as a thermoelement. Previously, these sensors were disposable and could not be restored, but today reusable models have appeared. In them, under the influence of temperature, the bimetallic element, changing its shape, affects the contact.
There are magnetically controlled samples. The permanent magnet located in them changes its properties as a result of heating, which leads to the operation of the device.
When selecting a heat detector for a room, it is necessary that the threshold temperature value for them be higher than the average for the building by at least 10 ° C. This allows you to avoid false alarms.
Each device is designed for a specific controlled area. By the nature of its detection on:
Point thermal fire detectors, in turn, are available in two types:
The operation of the former is based on a change in the state of the thermoelement when the temperature rises to a threshold value. It is worth noting that in order to trigger, it is necessary that the detector itself heats up to the value specified in the technical specifications. And this will take some time.
This is an obvious disadvantage of the device, since it does not allow detecting a fire at the initial stage. This can be eliminated by increasing the number of sensors located in one room, as well as using other types of sensors.
Differential heat detectors are designed to monitor the rate of temperature rise. This made it possible to reduce the inertia of the device. The design of such sensors includes electronic elements, which affects the cost.
In practice, most often, these two types are used in combination. Such a maximum differential fire detector is triggered not only by the rate of temperature rise, but also by its threshold value.
Linear devices or thermal cables are twisted pairs, where each wire is coated with a thermo-resistive material. When the temperature rises, it loses its properties, which leads to a short circuit in the circuit and the formation of a fire signal.
The thermal cable is connected instead of the system cable. But it has one drawback - a short circuit can be caused not only by fire.
To eliminate such moments, linear sensors are connected through interface modules that ensure communication with the alarm device. Many of them are used in technological elevator shafts and other similar structures.
Thermal sensors from Russian companies are most widely used on the domestic fire-fighting equipment market. This is due to both the characteristics of alarm systems, regulatory requirements, and their reasonable prices.
The most popular are thermal fire alarm detectors:
The Aurora detector is a maximum differential non-addressable detector. It is used to detect fires in a room and transmit a signal to the control panel.
Watch a video about the product:
The advantages of this model include:
Its cost is more than 400 rubles, but it fully corresponds to the quality of the device.
Explosion-proof thermal detectors IP 101-3A-A3R are also classified as maximum differential. They are intended for use in heated rooms and can work with DC and AC loops.
The advantages of this model include:
The cost of this model is significantly lower and amounts to 126 rubles, which makes them accessible to a wide range of users.
Watch a video about IP 101-7 explosion-proof products:
There are many more different types. This is a thermal explosion-proof detector and many others. Which one to choose for a particular room depends on various factors, which will be discussed below.
Each thermal sensor has certain classification characteristics. They are usually reflected in technical documentation. We list those that you should pay attention to:
For example, for large premises, it is recommended to install thermal fire detectors with a linear detection zone. When choosing a device, be sure to pay attention to the response temperature; it should not differ from the average by more than 20 ° C. Sudden changes in the control zone are unacceptable, they can lead to false alarms
There is a list of documents regulating the use of fire fighting equipment. They indicate that heat detectors are acceptable for use in most industrial and residential facilities. But at the same time, there is a list of premises where their work is impractical:
The IP 101-15SP detector produced by Spetspozhinzhiniring JSC is designed to issue an electrical signal when the ambient temperature rises above a specified value by opening (closing) the fire alarm loop circuit and turning on the light indication on the detector.
Supply voltage: 8 to 28 VDC or AC;
Operation temperature: +54...+115°С;
Explosion protection marking: 1ExdmIICT4/T6 X;
Shell protection degree: IP68;
Designated service life: 10 years.
Depending on the type of cable entries, detectors are made in three modifications:
1) “Maximum thermal fire detector IP101-15SP-B12-XX” - the delivery set includes cable glands for installation
armored cable with a maximum armor diameter of 12 mm or a metal hose with a nominal diameter of 10 mm.
It is recommended to use a metal hose of the RZ-Ts-X brand with a nominal diameter of 10 mm.
2) “Maximum thermal fire detector IP101-15SP-B15-XX” - the delivery set includes cable glands for installation
metal hose with a nominal diameter of 15 mm. It is recommended to use a metal hose of the RZ-Ts-X brand with a nominal diameter
passage 15 mm.
3) “Maximum thermal fire detector IP101-15SP-T-XX” - the delivery set includes cable glands for installation in a pipe
wiring with thread G=1/2”, where XX is the class of the detector.
Depending on the response temperatures, detectors are divided into the following classes:
"Maximum thermal fire detector IP 101-15SP-B12-A2."
(When ordering, you must indicate the required class of detector IP 101-15SP. Specifying the temperature class is mandatory, since the same temperature falls within the ranges of different classes. The response temperature should, if possible, be in the middle of the range of the corresponding class).
| Name | Quantity for execution | Note |
| Detector | 1 | |
| Ring sealing: | ||
| Ø8 mm for cable 6-8mm | 2 | |
| Ø10 mm for cable 8-10mm | 2 | |
| Washer | 2 | |
| Cable entry | 2 | Type depends on modification |
| Stub | 1 | |
| Bolt | 1 | |
| Protective cap | 1 | |
| screw | 1 | |
| Bracket for heat detector 2551 with nut | 1 | Option, must be ordered separately |
| Passport | 1 | |
| Specialist. key | 1 | For the party |
| Terminal key | 1 | For the party |
| Magnet | 1 | For the party |
