Distributed temperature sensing (DTS) in oceanography

DTS in oceanographyThe technology of distributed temperature sensing (DTS) is based on the application of Raman scattering from a laser beam light through optical fibers to detect temperature parameters along a fiber optic cable. The thing is that temperature resolution plays a crucial role. Herewith, this feature makes it possible to efficiently use DTS systems in oceanography.

Even though oceanographic applications of distributed temperature sensing are not new but such observations are not often. The reason is the serious challenges of deployment, calibration, and operation in oceanographic environment conditions. Nevertheless, researchers have tested the DTS system to overcome oceanographic configuration, calibration, and data processing difficulties.

It should be noted that they also evaluate temperature errors of DTS for several common scenarios. Difficult conditions influence the whole process, thus, the researchers look for alternative calibration, analysis, and deployment methods for distributed temperature sensing.

Therefore, these errors will be reduced and the successful application of DTS systems will be increased in dynamic ocean conditions. The thing is that DTS technology allows for “continuously sampling at a relatively high temporal and spatial resolution for significant duration over broad spatial scales.”

Despite distributed temperature sensing is widely applied in environmental applications, the oceanographic area remains challenging and still relatively rare. The main purpose of new DTS development is the solution to common problems present in oceanographic deployments.

To be more precise, the researchers use 2 various DTS systems, 3 fiber optic cables, and 24 thermistors. All of them help to test cables and different calibration configurations and perform distributed temperature sensing. Test results enable them to improve future oceanographic deployments. Moreover, they aid to achieve the best possible temperature signal in difficult deployment and operational environments.

DTS technology is a relatively new oceanographic tool. It allows for detecting temperature across wide spatial and temporal scales. Herewith, the application of such a fragile DTS system in remote and dynamically complex conditions remains difficult. Moreover, sometimes it is impossible to perform distributed temperature sensing at all.

Additionally, DTS systems face challenges during the detection of air/sea boundary. The reason is the change of water level, for instance, tides, waves, surge, etc., when the fiber optic cable can be exposed. Finally, the new DTS has succeeded to detect the temperature variance between the air-sea interface.

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

Space fiber optic application: a short overview

FBG sensors in spaceNew fiber optic solutions provide high-definition and fast fiber optic systems for sensing that become very promising in several space applications. Such advantages as composites in design and lightweight materials make fiber optic sensors highly important for the aerospace industry leading to a great requirement in non-destructive testing.

To be more precise, the development of advanced materials results in the fact that fiber optic sensors are considered to be essential in the design, production of aerospace vehicles, as well as their non-destructive testing. Fiber sensors are regarded as systems with flexible, low-profile optical fibers that do not need electrical sources.

It is possible to use fiber optic systems at sharply curved areas installed within devices or mounted directly to electrical components. Even though fiber optic sensors are compact and lightweight, they allow for distributed sensing directly stress, strain, acoustic, or temperature.

Compared to conventional strain gauges, fiber optic applications offer critical information with high density and low additional cost for various measurement points. A company-manufacturer of fiber optic systems from the U.S. has presented fiber sensors for aerospace industries.

Such fiber optic sensors perform more than 1,000 strain or temperature sensing per meter of a conventional compact, lightweight sensors. Additionally, “the high definition data can fully map the contour of strain or temperature for a structure under test or during manufacturing.”

These fiber sensors are suitable for dynamic applications or where lower sensor density is needed offering high-speed multipoint sensing, with tens or hundreds of fiber optic sensors on versatile optical fibers that cover long distances. Herewith, they provide the opportunity to perform several measurement types, for example, strain, temperature, vibration, or displacement by a single optical fiber.

Fiber optic applications include the aerospace industry and offer a more detailed design validation at every stage of the structural integrity building block process. It should be noted that composites provide a high level of strength-to-weight ratios. Nevertheless, new devices for validating the performance of fiber sensors are needed for their unique properties.

The compact size and distributed sensing of fiber optic sensors enable in-situ characterization for coupon testing, curing process validation, components/module testing as well as full-scale structural health monitoring of complex structures. It is possible to apply these fiber sensors in the predictive maintenance of smart elements.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, fbg strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

New FBG sensors with copper and aluminum coatings

copper FBG sensorsResearchers-manufacturers of fiber optic solutions from the U.S have presented new fiber Bragg grating sensors (FBG sensors) with copper and aluminum coating. Herewith, this fiber optic system has a compact size, it is hermetically sealed, and can maintain high temperatures leading to new opportunities for metal-coated fiber optic sensors.

To be more precise, FBG sensors and gold-coated sensors allow for developing new “inherently humidity-proof strain, temperature, displacement, acceleration, pressure, load, tilt, bio, and other useful fiber sensors and systems.” The researchers claim that FBG technology is considered to be very useful for numerous sensing applications in harsh environmental conditions because of its benefits provided.

The benefits of FBG sensors include the ability of absolute temperature measurement, rapid response, numerous sensing points on a single optical fiber strand with minimal mechanical burden and intrusion, as well as EMI immunity, spark-free, and chemical inertness.

Nonetheless, such conditions as a high level of humidity or temperatures, corrosive chemicals, or strong mechanical stress often presented in real environmental conditions create obstacles for fiber optic sensors with glass coating. New FBG sensors with copper, aluminum, and gold coatings enable researchers to enlarge current applications and develop new ones.

It should be noted that such processes as stripping and recoating are necessary for all laser writing methods included metals. The researchers demonstrate a robust technique to produce fiber sensors with acrylate, polyimide, aluminum, copper, and gold coatings installed into conventional high-temperature fiber Bragg gratings, which then are recoated with acrylate, polyimide, or gold coatings. 

Thus, such FBG technology makes it possible to change lengths of window stripping and recoating as well as control material thickness and length. Different types of inscription and coating allow for employing FBG sensors in different conditions from the cryogenic temperature of -200℃ to the high temperatures of +1000℃. 

These FBG sensors have a metal coating, and they are created by excimer and/or femtosecond laser writing methods. Additionally, the fiber optic system has been already tested, and the results show specific benefits in offering multipoint and multifunction sensing abilities in a constantly expanding range of applications not previously addressable by standard FBGs. The thing is that the coating of properly designed fiber optic sensors plays a crucial role in the integrity, survivability, functionality, and durability of FBG sensors.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, fbg strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

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

Distributed temperature sensors of high precision for Raman-based sensing

DTS for Raman sensingA new distributed temperature sensor (DTS) system has been developed to perform optimization of the temperature precision with the enhanced temperature sensitivity of backscattered spontaneous Raman scattering. The DTS system is based on the difference in sensitive-temperature compensation. 

Distributed temperature sensors apply the dual-demodulation, self-demodulation, and double-end configuration principles. The DTS system has been already tested and demonstrates great results: the temperature precision is considered to be 12.54 °C, 8.53 °C, and 15.00 °C along the 10.8 km under the traditional R-DTS systems, respectively.

It is possible to use the sensing system with difference sensitive-temperature compensation for the dual-demodulation, self-demodulation, and double-end configuration R-DTS, herewith, this fiber optic sensing technology enables to make the temperature precision better than 1 °C for these three demodulation systems.

The operating principle of Raman Distributed Temperature Sensor is based on “specific optical effects along the sensing optical fiber to obtain a spatially distributed temperature profile”. Compared to traditional discrete sensing techniques, R-DTS systems provide unique attributes and capabilities.

It should be noted that spontaneous Raman scattering of distributed temperature sensors uses the energy exchange in the optical fiber, therefore, when the pulsed light quantum and fiber optic material molecule leads to an inelastic collision in optical fiber, this will create an anti-Stokes light.

The thing is that the anti-Stokes light is regarded to be very sensitive to the surrounding temperature, and it allows modulating the environmental temperature using the principle of Raman scattering. Nowadays, such DTS systems find their application in the temperature safety monitoring thanks to the benefits of distributed measurement, long-distance, and high spatial resolution, as well as in transport infrastructure, smart grid and gas pipeline, etc.

It is necessary to pay on the following parameters when you choose distributed temperature sensors with high-performance: temperature precision, temperature resolution, and spatial resolution. DTS systems can be used as an industrial temperature measurement system, for instance, the carrier density in the power cable can be measured by employing a specific temperature. Additionally, distributed temperature sensors allow locating the position of pipeline leakage.

Tests demonstrate that the temperature demodulation system based on distributed temperature sensing offers higher temperature precision and resolution of the self-demodulation than the dual-demodulation system due to the signal-to-noise ratio. Moreover, the double-ended configuration for DTS systems allows avoiding the measurement error based on the change of local external attenuation.

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

High resolution distributed temperature sensing

high-resolution DTSThe fiber Bragg grating distributed temperature sensing on gas-insulated line spacer influences surfaces charge accumulation. Nevertheless, it is very difficult to perform the DTS measurement because the traditional electric sensors have huge dimensions, they are difficult to multiplex and highly sensitive to electromagnetic interference.

Thus, a distributed temperature sensing system of the GIL spacer based on the technology of the optical frequency domain reflectometry was designed to solve the challenges. The operation of the DTS system is based on the ultra-weak fiber Bragg grating or FBG technology to change single-mode optical fiber because of its higher signal-noise ratio.

It should be noted that the distributed temperature sensing also used the demodulation technique to compensate for the nonlinear frequency tuning errors caused by the unstable tunable laser. Therefore, the DTS system allows determining the connection between the space temperature and the wavelength shift during the calibration test.

Additionally, the distributed temperature sensing includes the application of the data processing technique for 3D surface temperature on a cone-type spacer. Finally, the DTS system based on FBG technology enables to obtain efficiently high-resolution temperature measurements on the spacer surface with the help of the optical frequency domain reflectometry, which is virtually impossible to perform with the traditional electric temperature sensing systems.

Nowadays the technology of direct current transmission with the gas-insulated line is an effective way due to its low electrical losses compared with, for example, AC transmission. That is why the distributed temperature sensing is considered to be a key factor that should be known first.

To be more precise, the disadvantages of traditional electric sensing systems such as dimensions, multiplexing, and sensitivity to EMI are solved by optical fiber sensing in electrical engineering. Fiber Bragg grating technology is a precise optical temperature sensing technique widely applied. But there are some limits in the multiplexing ability of conventional FBG sensors.

The new distributed temperature sensing system includes ultra-weak fiber Bragg gratings providing a reflectivity of only 0.1% compared to the conventional FBG sensors. Compared to the optical frequency domain reflectometry based on the Rayleigh technology, “ultra-weak FBG can achieve higher signal-noise ratio since the reflection of ultra-weak FBG sensor is much higher than the backscattering in the optical fiber”.

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

The development of fiber Bragg gratings using highly doped aluminosilicate glass optical fibers

FBGs made of doped fibersThe continuous development of high-temperature fiber Bragg grating technology (FBG technology) promotes a significant increase in novel applications. For instance, nowadays FBG applications include such fields as “the temperature profiling of high-temperature manufacturing equipment, monitoring of fuel combustion machinery, temperature regulation of large diesel engines in trains, as well as assessment the structural integrity of a building post-fire”.

Additionally, high-temperature FBG technology is used in oil and gas industries where the resistance to the temperatures higher than 500 °C is totally recommended. To be more precise, the sensors based on fiber Bragg gratings are able to stand temperature conditions below and above 800 °C. Herewith, the thermal stability of FBG sensors depends closely on the intrinsic thermal stability of the core-cladding materials.

This is the reason why the development of fiber optic technology with higher thermal resistance, for example, the molten core technique, is still required. Thus, it was decided to apply a circular core/cladding glass optical fiber containing a yttrium-doped aluminosilicate core and a silica cladding in FBG sensors that may withstand about 900 °C. 

The following types of FBG sensors are based on the nature of refractive index modifications induced by laser irradiation. The following types of FBGs  are distinguished:

  • The type I in fiber Bragg gratings produces a laser irradiation regime that emits an isotropic increase of the refractive index.
  • The type II in FBGs, in its turn, has a connection with the creation of an anisotropic index change upon irradiation, generally emitted by the presence of nanogratings, and leads to the observation of form birefringence.
  •  Ultra-high temperature regenerated fiber Bragg gratings are able to operate above 800 °C in silica optical fibers. Therefore, these FBGs find their application in such areas as the profiling of high-temperature manufacturing equipment, dual pressure/temperature sensing for gas turbines, sodium-cooled nuclear reactors, high-temperature air flow meters for internal combustion engines and train engine temperature regulation.
  • Femtosecond fiber Bragg gratings are made by ultrafast laser systems usually in the NIR spectral range, resulting in their use as temperature sensors for monitoring fluidized bed combustors, as well as for radiation-resistant temperature sensors.
  • Sapphire fiber Bragg gratings allow achieving even higher temperature operation by using materials with higher melting points.

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

Distributed temperature sensing for the fog detection

DTS for the fog detectionTraditional in situ observations of meteorological variables are limited by surface levels, herein, it is possible to carry out the lowest observation around just 1-m height. Therefore, observation results of both shallow fog, and the initial growth stage of thicker fog layers can be missed in this case. Nevertheless, the use of distributed temperature sensing or DTS technology allows measuring temperature and humidity parameters at centimeter resolution in the lowest 7 m.

It should be noted that it is very important to obtain high-resolution observation for radiation fog, and DTS sensors solve the problem. Two techniques are applied to make tests in the near-surface layer at a higher resolution than the traditional sensing devices.

Distributed temperature sensing is ideal for the measurement temperature and relative humidity parameters. DTS technology offers a high spatial and temporal resolution. DTS application includes detection of surface temperature and soil heat fluxes, the radioactive skin effect at the surface of water bodies, the Bowen ratio, near-surface turbulent fluxes under varying stability, and wind speed.

The combination of distributed temperature sensing with unmanned aerial vehicle provides the observation of the morning boundary-layer transition from stable to unstable conditions. Compared to traditional sensing techniques, DTS technology has a great advantage for studies of the stable boundary layer that is the resolution of steep gradients.

DTS sensors are able to detect shallow cold pools at high resolution that is the mark of radiation fog formation. The thing is that the fog presence causes elevated DTS temperatures of up to 0.7 ℃ when compared to traditional temperature parameters. However, the technology of distributed temperature sensing is required to be further tested to provide its reliability under stable, foggy conditions.

DTS devices enable to measure temperature characteristic along with optical fiber cables that are based on the backscattered signal of a laser pulse. The DTS sensors were tested, herewith, the optical fiber includes two multi-mode cores, while a simple single-ended (non-duplexed) configuration is applied for the measurements.

Finally, even in the conditions of fog formation absence, compared to DTS technology traditional sensing devices are not able to measure the strong temperature inversions in the lowest 1 m of air. Distributed temperature sensing provides an efficient solution to the problem.

The application of DTS systems is not limited by fog detection, but the broader near-surface (stable) boundary layer. Additionally, DTS sensors offer a better physical understanding of such processes as the collapse of turbulence at the onset of the stable boundary layer, intermittent turbulence within the stable boundary layer, and the transition between different boundary-layer regimes due to the ability of distributed temperature sensing to catch steep gradients in both temperature and relative humidity parameters.

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

Distributed temperature sensing of fiber optics under harsh conditions

DTS in harsh conditionsAccording to a recent study, the technology of distributed temperature sensing allows demonstrating the mechanical properties of fiber optics under harsh conditions. The fact is that numerous land and undersea oil procedures depend heavily on distributed temperature sensing for providing safety and functionality in severe environments.

Usually, the manufacturers use silica-based fiber optics for distributed temperature sensing and distributed acoustic sensing, where temperature and acoustic signals are transmitted and recorded continuously along the length of fiber sensor cable. Such fiber optic solution for FBG interrogator of 15 km length enables well and pipeline operators to apply fiber-based distributed sensing technology to measure the whole wellbore or pipeline span with a resolution of 1 m or less virtually in real-time.

For example, the technology of distributed temperature sensing with fiber optics is used in the operation of steam-assisted gravity drainage or SAGD technique, in which the main goal is the production of heavy crude oil and bitumen materials. Nevertheless, it is only one example, while distributed temperature sensing has numerous fiber optic applications.

It should be noted that the distributed temperature sensing system monitors the following extreme environments while optical fiber operation: high temperatures and pressures, ionizing radiation, and aggressive chemicals in the environment. However, in order to be applied in such severe conditions, fiber optics have to be highly reliable, while transmitting optical power with a minimum of added signal loss.

Most of the fiber sensor cables used in fiber optic applications contain a silica-based core and cladding because of the silica benefits that include high optical fiber transmission, superior thermal stability, and mechanical reliability. Herewith, the use of a polymer coating in fiber cables provides the mechanical protection of fiber optics and minimization of bend-induced optical attenuation.

The technology of distributed temperature sensing also enables to detect the factors limiting the performance of fiber optic cables at elevated temperatures and/or in aggressive conditions. The most frequent failures for fiber optics are related to added attenuation or loss of mechanical strength. Herewith, failure criteria differ from each other and depend on the type of fiber optic application.

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

FBG sensors: a comprehensive review

FBG sensorsA fiber Bragg grating is an optical interferometer embedded in an optical fiber. At the same time, fiber optics combined with certain substances (usually germanium) can change its refractive factor when the fiber is exposed to ultraviolet light. If such a fiber is illuminated with ultraviolet light with a specific spatial periodic structure, the optical fiber becomes a kind of diffraction grating. In other words, this optical fiber will almost completely reflect the light of a certain, predetermined range of wavelengths, and transmit light of all other wavelengths.

Application of FBG sensors

The FGB application includes the following fields:

  • Point sensors (that is able to measure deformation, temperature, pressure, tilt, displacement), embedded in composite materials and others;
  • Laser systems and amplifiers (filters, mirrors);
  • Telecommunications (dispersion compensation modules, WDM technology);
  • Research and development.

Difference between electrical and fiber sensors

For decades, electrical sensors (tensor-resistive, string, potentiometric, etc.) have been the main method of measuring physical and mechanical phenomena. Despite their widespread use, electrical sensors have several disadvantages, such as loss during signal transmission, sensibility to electromagnetic interference, the need to organize a spark-resistant electrical circuit (if there is a danger of explosion). These mentioned above limitations make electrical sensors unsuitable or difficult to use for a number of applications.

The use of fiber optic sensors is an excellent solution to these problems. In fiber optic sensors, the signal is light in the optical fiber instead of electricity in the copper wire at traditional electrical sensors.

Over the past twenty years, a huge number of innovations in optoelectronics and in the field of fiber optic telecommunications has led to a significant reduction in prices for optical components and to a significant improvement in their quality. This factor allows fiber optic sensors to move from the category of experimental laboratory tools to the category of widely used devices in various areas.

Operating principle of Bragg gratings

A fiber Bragg grating or FBG acts as a sensitive element of point fiber optic sensors, which is capable to reflect certain wavelengths of light and transmit all others.  This effect is achieved by periodically changing the refractive index in the core of the fiber optics.

When the laser light passes through an optical fiber, a part of it is reflected from the fiber grating at a certain wavelength. This peak of reflected light is registered by measuring equipment. As a result of the numerous parameters influence, the interval between the FBG bundles and the refractive index of the fiber optics change.

Consequently, the wavelength of the light reflected from the fiber Bragg grating changes. In addition, it is possible to determine the exact characteristics of the changes by changing the wavelength. In fiber optic sensors based on Bragg gratings, the measured value is converted to a Bragg wavelength offset. The recording system converts the wavelength offset into an electrical signal.

The sensing element of such FBG sensor does not contain electronic components and therefore it is completely passive, which means it can be used in the area of increased explosiveness, aggressiveness, strong electromagnetic interference. Numerous fiber Bragg gratings can be installed on a single fiber, each of which gives a response at its own wavelength. In this case, instead of a point sensor, we get a distributed sensing system with multiplexing along the wavelength.

The use of the light wavelength as an information parameter makes the FBG sensor insensitive to the long-term changes of the parameters of the source and radiation detector, as well as random attenuation of power in the optical fiber.

Common types of FBG sensors

The following types of fiber optic sensors  based on FBG technology are used for automated monitoring:

The principle of FGB sensor operation is based on the modulation of one or several properties of a propagating light wave (intensity, phase, polarization, frequency), which change occurs with a change in the measured physical quantity.

The basis of fiber-optic sensing technology is an optical fiber – a thin glass thread that transmits light through its core. The optical fiber consists of three main components: core, shell, and coating. The shell reflects the scattered light back into the core, allowing light to pass through the core with minimal loss.

It can be achieved by a higher refractive index in the core relative to the shell, resulting in a complete internal reflection of light. The outer coating protects the fiber optics from external influences and physical damage. It can consist of several layers depending on the required protection.

Benefits of fiber sensors based on Bragg gratings

The advantages of FBG sensors include:

  • Wide sensing range;
  • Possibility to integrate the FBG sensing system into the object structure;
  • Full fire and explosion safety;
  • Long-distance signal transmission;
  • Integration of several fiber optic sensors in one channel;
  • Insensitiveness to electromagnetic and radio frequency influences;
  • No need for recalibration (stable over time under constant external conditions).

Bridge, Australia, BridgeAt the moment, most of the sensors used in the world are electrical sensors. As it was mentioned above, in optical sensors based on fiber Bragg gratings, the signal is light passing through an optical fiber (instead of an electric current passing through a copper wire). This fundamental difference allows FBG sensors to overcome many problems typical for electrical sensors.

Features of fiber optic sensors

Optical fibers and sensors are non-conductive, electrically passive, and immune to electromagnetic interference. Monitoring with a tunable high-power laser system allows sensing over long distances with virtually no signal loss. In addition, each optical channel is able to monitor a variety of FBG sensors unlike the electrical channel, which significantly reduces the size and complexity of such a sensing system.

Optical sensing systems are ideal for use in conditions where conventional electrical sensors (strain gauge, string, thermistor, etc.) can be difficult to use (long distances, EM fields, explosion safety, etc.).  It is easy to switch to fiber optic solutions since the installation and operation of optical sensors are similar to traditional electrical sensors.

Understanding the principles of FBG operation and the benefits of Bragg grating sensor applications can greatly facilitate the solution of various problems in the field of sensing measurement (for example, monitoring of structures).

Nowadays FBG sensors are applied in various fields that require precise and fast measurements. Fiber Bragg sensing systems can be used in aeronautic, automotive, civil engineering structure monitoring, undersea oil exploration, in the mining industry, geotechnical engineering, structural engineering, tunnel construction engineering, etc.

Bragg sensors in medicine

The most promising application of FBG sensors is medicine. Now FBG technology is highly used for fiber-based biomedical sensing including biosensing, safety or security, and structural health monitoring. FBG sensors offer a new and effective way of real-time measurements. They can be applied in laser systems, medical tiny intra-aortic probes, and body sensors for biochemical analysis making.

For example, today fiber Bragg gratings apply optical-fiber sensing probes that are able to dissolve due to such ability as controlled solubility in a physiological environment. Thus,  FBG technology enables safer diagnostic of sensitive human organs and there is no need for a surgical extraction. The development of FBG continues, and it is possible that very soon new FBG sensors with improved characteristics appear.

How to choose the right fiber optic product?

If you want to obtain a highly efficient 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. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com