Specialists distinguish a large number of varieties of cable products. But a separate class includes 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 environmental conditions change. The sensitive elements are so visible that they can be freely fixed. Compared to other cables and sensors, such devices are not unified, so there are no uniform standards for them.
Application features
Many events have a large number of fire safety issues due to their complex configurations, operating conditions, temperature and other difficult features.
For example, under the condition of strong electromagnetic problems, smoke at the facility, high radiation, many temperature and smoke sensors and flame detectors cannot function normally and give a signal about the presence of an accident onproduction. In many cases, the use of a linear fire detector is really justified, and in some cases there is not even a replacement for them, for example, when used in a nuclear reactor.
Thermal cables can be used almost everywhere, but they can be especially effective in cable routes, collectors, elevator shafts, garbage chutes, tunnels, tanks with combustible and lubricant components, tunnels and transport stations. With 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 degrading its performance, it can additionally 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 monitor the temperature in particularly hard-to-reach places. In this case, it is important that the cable is laid on the very surface of the equipment.
Instrument operation
Structurally, the thermal cable includes a twisted pair, which is made of steel wire. Each wire is twisted into a twisted pair and coated with special heat-sensitive polymers.
Because of this, there is a high voltage in the cable, which, if there is a problem with the insulation, leads to a short circuit.
The principle of operation of the IP thermal fire detector for fire alarms is that when a certain temperature regime is reached, the sensitivity to heating of the insulation is broken, and the wires are connected under the influence of internal voltage, as a result of which a short circuit occurs. In order for the thermal cable to be activated, it is enough for overheating to occur in just one area. The total line resistance changes 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.
Main types of sensors
All thermal fire detectors according to the sensor reaction can be divided into maximum, which give a reaction to the set temperature, differential, which start working when it changes from the set parameters, as well as maximum differential sensors, which give a reaction to two at once these factors. All of them are contact, electronic, optical, and also mechanical.
Mechanical sensors
The maximum thermal fire detector when monitoring the state of the device calculates the dependence of pressure on the ambient temperature. The sensor in the device contains 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 incoming indicatorsof the detector to the temperature and, if the set parameters are exceeded, they send an alarm signal to the fire panel. Such types 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 from temperature-sensitive polymers. The number of wires may be more than a few. The outer shell can be made from different materials, this will directly depend on the area of \u200b\u200bits use.
In the zone of ignition and overheating, the cable insulation begins to melt, which provokes a short circuit. The well-designed interface module helps to determine the line resistance and the total distance to the wire short.
Electronic sensor
Unlike contact linear detectors, linear electronic sensors do not provoke a short circuit during operation of the device, 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 multi-core 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 transmits an alarm signal to the fire panel.
Optical sensor
Features of the operation of the optical sensor in a linear thermal fire detector are based on a change in the optical transparency of the sensor, which directly depends on the ambient temperature. For this, a fiber optic cable is used. 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 detects the power of the direct and reflected color, the speed of its change and the detection of the temperature in the area where the problem occurred.
Depending on the type of fiber used and the settings of the processing module, the equipment can perform many thermal sensor functions.
Most Popular Devices
The most popular and widely used thermal cables include the following models:
- Protectowire;
- Thermocable;
- "Special device";
- "Fire Technician";
- "Etra-Special Automatic".
Thermal cables from Protectowire have been on the market for over 10 years. For the past four years, manufacturers have been producing contact-type fire alarm cable.
The features of the devices and their cost do not differ much, the differences are in the cable resistance of only 1 meter, maximum length, voltage and overall range. Depending on the purpose of using the device, you can find a better and more convenient cable for yourself.
Recently, models of electronic type thermal cables are often produced. They include a cable up to 24 centimeters long witha temperature sensor installed inside the braid, in some models an additional sensor is built in, which helps to detect carbon monoxide nearby. Unlike contact linear devices, they function in exactly the same way as thermal devices.
Mounting Features
There are many ways to mount a fire heat linear detector. As a rule, the same requirements are imposed on a thermal cable as on a simple point thermal sensor. The installation of the fire alarm detector is carried out using special fasteners, which are included with the purchase of 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 cable insulation and, as a result, a false circuit. If the cable includes several pieces at once, then special terminal connectors are used.
This 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 suspension cable should be used.
When laying the detector, it is important to remember the technological characteristics of the premises, for example, in warehouses, it is important to take into account the functioning of unloading and loading devices.
It is important to install the cable with a stretch and at a room temperature of at least -10 degrees Celsius, but such a device will work at temperatures from -40 to +125 degrees Celsius. When installing the safety detector on flat ceilings, the distance between adjacent cablesmust not exceed 10.6 meters.
Manufacturer's requirements
In addition, there are special requirements from the device manufacturer. To ensure its normal functioning, it is important to comply with them. The cable should not be allowed to touch any objects, as this will prevent it from responding normally to temperature changes in the environment. Objects in close proximity to the detector can act as a heat sink, causing various malfunctions in the device.
The quality of the installation of a thermal linear fire detector at the event will directly affect its safety and performance. All technical means with the help of sensors built into them help to identify the source of ignition and prevent a fire in time. The technical requirements for such devices continue to grow. The advent of new detectors that help identify areas of fire contributes to the timely and accurate detection of a fire.
Where the devices are used
Thermal linear fire detectors are commonly used at the following facilities:
- heated and unheated rooms;
- outdoor objects, including linearly extended ones;
- Events with long ceilings, such as production halls, shopping malls, sports stadiums, theaters, concert halls, sewers, 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 environments with low or high temperature, high humidity, dust, and vibration.
Heat detector "Bolid"
Linear thermal fire detector "Bolid" is an optical installation, which includes a receiver and 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 developments of detectors include a self-monitoring system that helps to amplify the applied signal during dusting of optical devices. The cost of the heat detector Bolid is quite high (starts from 4000 rubles), but at the same time the device has a minimum number of wires, and it is also very quickly mounted.
Address fire detector "Bolid". This type of sensor helps to receive and transmit signals through the radio channel, the total range of the device reaches 600 meters.
Thermocable GTSW 68
Fire Thermal Linear Detector The GTSW 68 thermal cable is used to control the threshold temperature and detect the ignition source to prevent a fire at the facility. The device regulates the temperature along its entire length and can be combined with MIP modules.
Heat cable includescable that helps to identify the source of overheating in any area. The detector has only one continuous sensor, which is used when the conditions at the enterprise do not allow the installation of a simple sensor, and if there is a risk of explosion, the use of a thermal cable is considered the best way out.
The PHSC 155 fire thermal linear detector 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 permanent sensor.
