Specialists distinguish a large number of varieties of cable products. But in a separate class include a linear thermal fire detector, which is used in hardware and software systems for monitoring the state of nuclear power plants. The sensitive element in such a device is located along the entire length of the cable, it can change its electrical parameters when changing environmental conditions. The sensitive elements are so noticeable that they can be freely fixed. Compared to other cables and sensors, such devices are not unified, therefore, there are no uniform standards for them.
Application features
At many events, there are a large number of fire safety problems due to their complex configurations, working conditions, temperature, and other difficult features.
For example, subject to strong electromagnetic problems, smoke in the facility, and high radiation, many temperature and smoke detectors and flame detectors cannot function normally and give a signal about an industrial accident. In many cases, the use of a linear fire heat detector is really justified, and in some cases it does not even have a replacement, for example, when used in a nuclear reactor.
Thermal cables can be used almost everywhere, but they can be very effective on cable routes, collectors, elevator shafts, garbage chutes, tunnels, tanks with combustible and smear components, tunnels and transport stations. With the help of a large temperature range, fire heat detectors can be used in freezers, refrigerators, elevators, hangars and some industrial events.
Since the thermal cable can be used in buildings with large electromagnetic fields without compromising performance, it can also be used to control the quality of heating devices (for example, generators, tomographs and transformers).
Due to the special flexibility and small diameter of the cable, the thermal fire detector helps to track the temperature in particularly hard-to-reach places. In this case, it is important that the cable runs along the surface of the equipment.
Device operation
Structurally, the thermal cable includes a twisted pair, which is created from a steel wire. Each wire is screwed into a twisted pair and coated with special heat-sensitive polymers.
For this reason, there is a high voltage in the cable, which leads to a short circuit in case of insulation problems.
The principle of operation of the IP heat detector for fire alarms is that when a certain temperature is reached, the sensitivity to heating the insulation is violated, and the wires are connected under the influence of internal voltage, resulting in a short circuit. To activate the thermal cable, it is enough that overheating occurs in only one area. The total line resistance is changing rapidly. A special controller is responsible for the conductivity of the cable, determines the exact area of its ignition, compares it with the settings and redirects the alarm signal to the bullets of the anti-protective device.
The main types of sensors
According to the reaction of the sensor, all thermal fire detectors can be divided into maximum, which give a reaction to the set temperature, differential, which begin to work when it changes from the set parameters, as well as maximum differential sensors, which give a reaction to these two factors at once. All of them are contact, electronic, optical, as well as mechanical.
Mechanical sensors
The maximum thermal fire detector, when monitoring the state of the device, calculates the dependence of pressure on the ambient temperature. In the sensor in the device is a special copper tube with compressed gas. An increase in temperature indicates a change in pressure in the tube, which is indicated on the sensor itself. The measuring unit changes the detector’s incoming indicator to the temperature and, when the set parameters are exceeded, send an alarm to the fire panel. Such varieties of mechanical sensors are almost never used due to the complexity and development of more technologically advanced and modern sensors.
Contact devices
Contact sensors in linear detectors represent with you a twisted pair of steel wires, which are made of polymers sensitive to temperature conditions. The number of wires may be more than a few. The outer shell can be made of different materials, this will directly depend on the area of their use.
In the area of ignition and overheating, the cable insulation begins to melt, which provokes a short circuit. A module with a well-designed interface helps determine the line resistance and the total distance to the point of wire closure.
Electronic sensor
Unlike contact line detectors, linear electronic sensors do not provoke a short circuit during device operation, they read all changes in resistance from the ambient temperature and transfer them to the control and measuring device.
The sensitive element includes a large number of sensors that are installed in a multicore cable, through which all information passes from each element of the line. The receiving unit processes the received signals and compares them with the alarm parameters set in it. When a critical situation is detected, the device sends an alarm signal to the fire panel.
Optical sensor
The features of the optical sensor in a thermal fire line detector are based on a change in the optical transparency of the sensor, which directly depends on the ambient temperature. Fiber optic cable is used for this. At that moment when the light from the laser falls on the place of ignition or overheating, part of it is immediately reflected. The processing device reveals the indicator of the power of direct and reflected color, the speed of its change and the identification of the temperature indicator in the area where the problem occurred.
Depending on the type of optical fiber used and the settings of the processing module, the equipment can perform many functions of a heat sensor.
Most popular devices
The following models are among the most popular and widely used thermal cables:
- Protectowire;
- Thermocable
- "Special device";
- "Pozhtekhnik";
- "Etra-special automatic."
Protectowire thermal cables continue to go on sale for 10 years. For the past four years, manufacturers have been manufacturing a thermal cable for contact type fire alarms.
The features of the devices and their cost do not differ much, the differences are in the cable resistance of only 1 meter, the maximum length, voltage and the general range. Depending on the purpose of using the device, you can find a better and more convenient cable for yourself.
Recently, models of thermal cables of the electronic type are often produced. They include a cable up to 24 centimeters long with a temperature sensor installed inside the braid; in some models, an additional sensor is built-in to help identify carbon monoxide nearby. Unlike contact, linear devices function in exactly the same way as thermal devices.
Mounting Features
There are many ways to install a fire heat line detector. The thermal cable, as a rule, has the same requirements as a simple point thermal sensor. The installation of a fire alarm detector is carried out using special fasteners that are included when purchasing the device or are recommended for purchase by the manufacturer of the thermal cable. It is important to buy special fasteners, as this will help to avoid problems with the insulation of the cable and as a result of a false circuit. If the cable includes several pieces at once, then special terminal connectors are used.
Such a cable is installed under the ceiling or on the walls. In the place where there are some problems with laying the thermal cable, a specialized cable suspension should be used.
When laying the detector, it is important to remember about the technological characteristics of the room, for example, in warehouses it is important to consider the functioning of unloading and loading devices.
It is important to install the cable with a stretch and at a room temperature not lower than 10 degrees Celsius, but such a device will perform work at a temperature of -40 to +125 degrees Celsius. When installing the safety detector on even ceilings, the distance between adjacent cables should not exceed 10.6 meters.
Manufacturer requirements
In addition, there are special requirements from the device manufacturer. To ensure its normal functioning, it is important to follow them. The cable should not be allowed to touch any objects, as this will not allow it to react normally to changes in temperature in the environment. Items in close proximity to the detector can play the role of a radiator, leading to various malfunctions in the operation of the device.
At a high-quality installation of a fire thermal linear detector at an event, its safety and performance will directly depend. All technical means with the help of sensors built into them help to identify a source of ignition and prevent a fire in time. Technical requirements for such devices continue to increase. The emergence of new detectors that help identify areas of fire, contributes to the timely and accurate detection of fire.
Where do they use devices
Thermal linear fire detectors are commonly used at the following sites:
- heated as well as unheated rooms;
- outdoor objects, including linearly extended;
- events that are distinguished by a long ceiling, for example, production shops, shopping malls, sports stadiums, theaters, concert halls, collectors, mines and tunnels, energy and transport facilities, including sea and river vessels.
The sensor with high sensitivity in the device can be installed in direct contact with the protective device, in hard-to-reach places and used in conditions with low or high temperature, high humidity, dust, and vibration.
Heat detector "Bolid"
The Bolid linear thermal fire detector is an optical installation, which includes a receiver and a transmitter. The device can be mounted in different corners of the building, in close proximity to the ceiling, determine the distance value (50-140 meters).
Modern detectors developments include a self-monitoring system, which helps to amplify the supplied signal during the dusting of optical devices. The cost of the Bolid heat detector is quite high (starts from 4000 rubles), but at the same time the device has a minimum number of wires, and it is also mounted very quickly.
Address fire detector "Bolid". This kind of sensor helps to receive and transmit signals through the radio channel, the total range of the device reaches 600 meters.
Thermal cable GTSW 68
Fire Thermal Line Detector The GTSW 68 thermal cable is used to control the threshold temperature and to detect a source of ignition to prevent a fire at the facility. The device controls the temperature along the entire length and can function in conjunction with MIP modules.
The thermal cable includes a cable that helps determine the source of overheating in any area. Only one continuous sensor is mounted in the detector, which is used when the conditions in the enterprise do not allow a simple sensor to be installed, and if there is a risk of explosion, the use of a thermal cable is considered the best way out.
The fire heat linear detector PHSC 155 is also very popular on the market. The system includes a cable that helps to identify the heat source throughout its length, it is also equipped with a special sensor of constant action.