Distributed temperature sensors promote warning systems

DTS for warning systemsTemperature is a key safety indicator in any industry. The technology of distributed temperature sensors using optical fiber allows measuring the temperature at any point in the fiber, with an interval of 1 meter, resulting in the detailed temperature dependence of all required areas. The data obtained by this technique makes it possible to develop intelligent warning systems based on it, therefore, replacing outdated point-based monitoring systems.

Operating principle of temperature sensors

The optical fiber itself acts like a fiber optic sensor, and the distributed nature of the DTS technology enables us to determine the temperature change at an arbitrary point, spreading many kilometers from it. Moreover, the measurement quality is not affected by electromagnetic radiation, thus, the distributed temperature technology is free from false alarms.

To be more precise, distributed temperature sensors (DTS) allow measuring the characteristics of an object along a fiber optic cable, while the fiber cable is a linear sensor, which is a continuously distributed sensing element throughout its entire length.

The operating principle is based on the reflectivity of stimulated Raman scattering of light (Raman effect). A semiconductor laser is also used to determine the location of temperature changes in a fiber optic cable. The fact is that the structure of the optical fiber changes when the temperature changes. 

When laser beam light from the laser system enters the area of temperature change, it interacts with the changed structure of the optical fiber, and in addition to direct light scattering, reflected light appears.

Benefits of temperature sensing systems

The main advantages of fiber optic sensors in comparison with classical analogs are the following:

  • Compact size;
  • Very fast response to parameter changes in the environment;
  • Low weight;
  • Multiple parameters can be registered simultaneously by a single distributed sensor;
  • Reliability;
  • Very wide operating temperature range of DTS;
  • Small price per unit length of the sensing system;
  • High sensitivity;
  • Long operating time;
  • The high spatial resolution of temperature sensors;
  • Resistance to chemicals and aggressive environments;
  • DTS is not affected by electromagnetic disturbances;
  • The sensitive part of the fiber sensor does not require connection to power lines.

The processing unit measures the propagation speed and power of both direct and reflected light and determines where the temperature changes. For instance, at a wavelength of 1550 nm, a pulsed generation mode is used with a laser power limit of 10 mW.

Types of sensors for temperature measurement

There are several types of optical fibers, each of which meets certain requirements for its properties, depending on the application due to the fact that the properties of the optical fiber can be varied over a wide range. 

Physical effects on the optical fiber, such as pressure, deformation, temperature change, affect the properties of the fiber at the point of exposure and it is possible to measure the environmental parameters by measuring the change in the properties of the fiber at a given point.

In general, a fiber optic sensor consists of two concentric layers: fiber core and optical coating. The fiber optic light guide part can be protected by a layer of acrylate, plastic, reinforced sheath, etc., depending on the application of this fiber cable.

Thus, distributed fiber optic sensors are perfect for industries related to combustible and explosive materials, such as coal, oil and gas production, etc. for use in fire alarm systems of various structures.

Common applications of DTS systems

Application of distributed temperature sensors includes:

  • fire alarm systems in the road, rail, or service tunnels;
  • thermal monitoring of power cables and overhead transmission lines to optimize production processes;
  • improving the efficiency of oil and gas wells;
  • ensuring the safe working condition of industrial induction melting furnaces;
  • monitoring the tightness of containers with liquefied natural gas on ships in unloading terminals;
  • detection of leaks in dams;
  • temperature control in chemical processes;
  • leak detection in pipelines.

In addition, DTS systems combined with other tools open completely new areas of application. For example, it is possible to design a specialized device – a fire detector based on a distributed fiber optic temperature sensor.

Temperature sensors for fire detection

Detecting a fire in an industrial environment is not an easy task because of the large number of disturbing factors, many of which can be considered by detectors as carriers of fire signs. In addition, dust deposited on the DTS‘ sensitive elements makes it difficult to operate and it can disable them.

It is also necessary to take into account the possible smoldering of the deposited dust, which can also lead to false alarms. The presence of fumes and aerosols makes it impossible to operate smoke optical-electronic fire detectors. The presence of carbon monoxide will trigger gas fire detectors.

Industrial facilities and production are characterized by large volumes of premises, high ceilings, the presence of long tunnels, collectors, mines, inaccessible areas, and premises with a complex configuration and geometry. And in these conditions, it is certainly possible to protect using traditional fire alarm systems, but this involves the use of a large number of detectors, and therefore they have high costs, including installation and maintenance of alarm systems and automation.

It is difficult to select detectors for explosive zones, especially for use in underground operations and mines. Aggressive media are often present in chemical industries. There are also objects of sea and river transport, characterized by the aggressive salt fog.

Oil and gas application

The use of non-electric sensing devices, the use of fiber optic cable allows the DTS to be applied in enterprises of the oil and gas complex, mines, underground operations, chemical industries (including those with aggressive environments), and metallurgy and energy enterprises.

As for oil companies, the active development of high-viscosity oil fields, which imposes strict requirements on the production equipment, and the severe depletion of most oil and gas fields require mining organizations to conduct prospecting and exploration operations, change production technologies and control the technical condition of wells.

The main task for mining companies to increase the well’s production capacity in real-time is to track information about the processes occurring in wells and fields. Solutions based on standard temperature sensors suggest well logging using point measuring instruments, which leads to the inaccuracy of the data obtained. 

The disadvantages of such sensing devices include the inability to fix the distribution of one of the most important parameters of the well – the temperature profile in real-time, as well as the need for power supply, the impact on the measurement results of external electromagnetic fields, labor and time costs required for the departure of the team and performing various operations, including the immersion of the fiber sensor element and its movement along the well, data processing, etc.

DTS as a part of a fiber optic system

The fiber optic sensing system consists of distributed temperature sensors designed to measure temperature along the borehole, and a point-to-point fiber pressure sensor. Optical fibers of a distributed temperature sensing system and pressure sensors can be structurally installed in a single fiber cable.

The fiber optic cable is resistant to mechanical damage. Additional fiber optic cable protection is not required during descent and lifting operations, but the protection of the fiber cable from mechanical damage during descent and lifting operations can be provided by the use of protective coatings.

Where to buy quality temperature sensors?

If you want to obtain a highly efficient distributed temperature sensing system, you should choose the Optromix company. Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for monitoring worldwide. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed acoustic sensing (DAS) systems, distributed temperature sensing (DTS) systems. 

Distributed temperature system provides continuous underground power lines monitoring of temperatures, detecting hot spots, delivering operational status, condition assessment, and power circuit rating data. This helps operators to optimize the transmission and distribution networks, and reduce the cost of operation and capital.

Usually, the DTS systems can detect the temperature to a spatial resolution of 1 m with precision to within ±1°C at a resolution of 0.01°C. Measurement distances of greater than 30 km can be monitored and some specialized systems can provide even tighter spatial resolutions.
The advantages of working with Optromix:

  • Our DTS system has the superior quality, however, its price is one of the lowest in the market;
  • Optromix is ready to develop DTS systems based on customer’s specifications.

If you are interested in DTS systems and want to learn more, please contact us at info@optromix.com

New concept of distributed fiber optic sensors

distributed FBG sensorsFiber optic technology promotes a new era of the Internet because optical fibers transmit huge amounts of data information all around the world. Herewith, fibers are regarded as an excellent platform for fiber optic sensors. It is possible to spread fiber sensors over hundreds of kilometers, simply install within structures, and even in a severe environment where the application of electricity is forbidden. Nevertheless,  optical fiber sensors have some inevitable problems as well.

The operating principle of an optical measurement is based on the light that touches the medium under test but conventional optical fibers are developed to perform the exact opposite. To be more precise, the design of optical fibers includes a glass cladding, with a much thinner, inner core. Herewith, the light is sent at the inner core, and every effort is made to keep light from leaking outside. “A substance under test, in most cases, lies outside the much larger cladding. Unfortunately, guided light does not touch upon much of the outside world.”

The only solution to the problem is coupling to the cladding modes that need for the inscription of permanent, periodic perturbations in the optical fiber medium (fiber Bragg gratings). FBGs are written at specific, discrete locations. Fiber optic sensor has limits to point-measurements only because their erasement or movement are prohibited. Optical fiber sensors are perfect in spatially-distributed analysis, in which every fiber optic segment operates as an independent measurement node. Additionally, it is possible to use two strong optical waves into the optical fiber instead as an alternative to the fiber Bragg gratings.

Also, there are Brillouin dynamic gratings, which can be switched on and off at will compared to standard FBGs. It is possible to short segments of arbitrary locations, and scan along with the optical fiber. The thing is that the developed distributed fiber optic sensor is considered to be a first of its kind. Researchers have overcome some challenges: they succeeded to demonstrate the accurate measurement of refractive index outside the cladding boundary of traditional, unmodified optical fiber resulting in an 8cm spatial resolution. Herewith, the analysis demonstrates proper identification of short fiber optic sections immersed in water and ethanol, and clearly distinguished between the two. 

The researchers claim that it is a new concept of distributed fiber optic sensors. Such fiber sensors allow overcoming a decades-long challenge: fiber optic sensors perform the distributed mapping of refractive index outside the cladding of conventional optical fiber, where light does not achieve. The applications of distributed fiber optic sensors include leak detection in critical infrastructure, and process monitoring in the petrochemical industry, desalination plants, food and beverage production, and more.

Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for the clients. Optromix produces a wide range of fiber optic devices, including cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Moreover, Optromix is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

FBG sensors prevent tunnel fire

FBG sensors for fire detectionTunnel fires are not regarded as usual, however, they also can perform great damage to lives and properties if they take place. The process of fire detection inside the lengthy and curved tunnel is challenging. Nevertheless, fiber optic sensors based on fiber Bragg grating or FBG technology allows detecting tunnel fires and FBG sensors are considered to be a novel methodology that determines not only the presence but also locates the fire inside the tunnel.

To be more precise, FBG sensors are installed across the inner sides of the tunnel where they control it by the optical spectrum analyzer or wavelength division multiplexing sensor interrogator at the exit. “The change in the center wavelength from the original spectrum at the output denotes the temperature change (fire occurrence) inside the tunnel.” FBG fiber optic sensors offer output with more precision, herewith, fiber Bragg gratings can hold very high-temperature values.

It should be noted that it is possible to detect fires applying various ways, for instance, installing temperature sensors inside the tunnel or controlling the tunnel through the camera. Temperature sensors enable to sense of tunnel fires but their location presents difficulties. Moreover, such a temperature sensor as a thermistor can not stand very high temperatures (1000˚C) as well as there is a problem of self-healing.

FBG sensors, in their turn, provide a highly efficient process of sensing and locating. The thing is that fiber Bragg gratings in fiber optic sensors lead to a narrow range of wavelengths to shift and the rest of it to transmit through it. The center of the reflected wavelength is Bragg’s Wavelength. The features of FBG sensors allow measuring temperature or strain changes in the structures. Additionally, FBG fiber optic sensors have a greater temperature steadiness ability, more immune to electromagnetic interferences, longer lifetime, explosion safe and it is possible to be multiplexed.

Fiber Bragg grating is a short part of optical fibers that reflects a specific light wavelength and transmits all other wavelengths. FBGs operate as an optical notch filter. The operating principle is based on the Bragg grating patterns inside the fiber that perform the reflection. The design of fiber Bragg gratings includes holographic interference or a phase mask to undergo a short length of optical fiber to a periodic distribution of light intensity. 

The developed FBG sensors have been already tested and demonstrated the following results: the sensitivity value of the fiber optic sensor achieves 20 pm/˚C. Also, it is possible to increase the accuracy of fire location inside the tunnel by increasing the number of FBG fiber optic sensors for the considered tunnel length of 4 km. Thus, FBG technology can help to perform operations very fast and can save many lives and properties.

Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for the clients. Optromix produces a wide range of fiber optic devices, including cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Moreover, Optromix is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

Totally new application of DAS systems

DAS for weevil detectionThe red palm weevil is regarded as a serious problem for the cultivation of date palms leading to massive economic losses worldwide. Although curative techniques are not challenging, early detection is still difficult to be performed. Fiber optic technology allows overcoming the threat and offers reliable detection of RPW by a distributed acoustic sensor (DAS).

Modern DAS systems enable to detect feeding sound created by larvae as young as 12 days, in an infected tree. Compared to traditional methods, the DAS technique provides a cost-effective and non-invasive alternative that can perform 24-7, real-time monitoring of 1,000 palm trees, or even more. Moreover, distributed sensors allow controlling temperature, a crucial characteristic to monitor farm fires, one more important problem for the cultivation of palm trees around the world.

Nowadays there are various techniques to detect the weevils. For example, it is possible to use trained dogs to smell the odor, however, such sensing is not precise and has low efficiency. That is why distributed acoustic sensors are considered to be the most promising early detection techniques. Current sensing technologies use sound probes to install them right into the tree trunk but such acoustic sensors damage plants and create a nest for other insects.

The novel distributed acoustic sensor combined with a signal processing algorithm offer a reliable solution for the early detection of red palm weevils. The design of the DAS system is based on the use of the laser and photodetector installed within a single unit, while only the optical fiber is wound around the palm trees to create an optical network. The developed DAS technique has been already tested on two palm trees (one healthy and one infested with ~12 days old larvae.).

The thing is that the novel distributed acoustic sensors are “uniquely non-invasive, providing 24-7 monitoring, at relatively low cost, and offering wide coverage of the farming area, using only a single fiber optic cable.”

To be more precise, all the optical/electronic components applied to design acoustic sensors are put into a sensing unit, which is linked to an optical fiber that is extended throughout the palm-trees farm. Herewith, the fiber circles each tree trunk, from the ground up to a ~1 m height because the probability of RPW is extremely high there. Also, the fiber optic cable between trees can be either put on the ground buried in the soil providing real-time monitoring that promotes precise identification of locations of the infected and healthy trees.

The design of DAS systems includes the use of phase-sensitive optical time-domain reflectometry (Φ-OTDR) that has numerous potential applications in the oil and gas industries as well as for real-time structural health monitoring. The operating principle of distributed acoustic sensors is based on “launching a train of optical pulses generated by a narrow linewidth laser into a single-mode fiber.”

Optromix is a DAS system manufacturer that provides top of the line distributed acoustic sensing systems suitable for monitoring of commerce networks. If you have any questions or would like to buy a DAS system, please contact us at info@optromix.com