Tag: FBG interrogators

Structural Health Monitoring Systems Applications

Structural health monitoring systems have found a number of applications in various fields. A complex approach including several techniques is the best solution for detecting damage and structural changes.

Here are some examples of its implementation in structures where fiber optic technology is more commonly used. Structural Health Monitoring Systems Applications

Structural Health Monitoring Common Information

The most effective methods of maintenance programs include early detection of material degradation and failure. Mostly, fiber optic systems have two purposes of applications:

Structural efficiency control during the construction;
Continuous monitoring of structural efficiency under service loads.

Structural health monitoring systems consist of three subsystems:

A network of fiber Bragg grating sensors;
An FBG interrogator that records the optical reflection from each fiber optic sensor. They are placed in the necessary locations, depending on the applications and type of the structure.
A processing unit that collects all the data from the FBG interrogator, processes it and transmits it to the user.

Distributed Sensing Systems

Distributed temperature systems are often the choice for harsh environments where traditional sensors may not be suitable. When we talk about dams, tunnels and similar structures, there are conditions that greatly affect the operation of the structures and sensors. Ground movement, earth pressure, water and groundwater have an impact on the reliability and efficiency of any monitoring system.

Specialists can monitor all deformations and temperature changes through distributed sensing. Distributed fiber optic sensors are capable of measuring various parameters from thousands of points and transmitting them to a center that provides complex data on any changes.

Distributed temperature systems are often the choice for harsh environments where traditional sensors may not be suitable. In the case of dams, tunnels and similar structures, there are conditions that have a major impact on the operation of the facility and its sensors. Ground movement, earth pressure, water and groundwater will affect the reliability and efficiency of any monitoring system.

Structural Health Monitoring of Dams

Dam safety can have a significant impact on the surrounding environment and people. That’s why structural health monitoring of the dams is an essential part of the dam safety regime. Timely detection of defects and minimizing the effects of possible damage are the main purposes of such systems. However, specialists may face some difficulties due to the height and complex structures of the dams. Comprehensive structural health monitoring can’t be fully achieved with just a few monitoring points; it requires a complete, properly designed fiber optic system. Another problem is that some areas of the dams are inaccessible or difficult to access.

There are a number of factors that can affect dam construction. These include temperature, hydrostatic pressure, chemical reactions, etc. There are also environmental factors such as air temperature, reservoir levels, and earthquakes.

All of these circumstances can be the cause of typical dam problems such as cracking, displacement, etc. The other problem is the appearance of internal erosion, which can cause the failure of the whole mechanism in the future. This problem is hard to detect. That’s why it is important to have an effective fiber optic system in place for structural health monitoring and therefore safe operation.

Accidents in dams usually occur during the first filling or in the first few years of operation. However, there are also accidents that occur later.

Structural Health Monitoring (SHM) of Tunnels

SHM is able to provide a quick assessment of the state of health of the tunnel. It is typically used for safety improvement and optimization of maintenance and operations activities. The fiber optic monitoring system provides data on any changes in indicators that could be the cause of tunnel collapse. This makes it possible to monitor the stability of the structure and take action when it’s needed.

The construction of tunnels is based on soil conditions, the functions of the tunnels themselves, and logistical issues. Underground construction is irreplaceable, especially in cities where land resources are scarce. They are not as susceptible to the effects of natural disasters as are structures on the surface of the earth.

In the hard-to-reach or problematic areas of the tunnels, distributed monitoring systems are usually recommended. This makes it easy for staff to monitor the condition of their structures and perform necessary maintenance in a timely manner. This is especially important when it comes to fires – the biggest danger in tunnels. There are special fiber optic systems for temperature control and early warning of ignition, including fiber optic heat detectors.

Today, there are automated fiber optic solutions that provide accurate monitoring from a remote location. These fiber optic devices are often designed specifically for use in critical locations. In addition, they consider the cases that may occur, such as the use of the additional FBG sensors. If the other sensor fails, they will be able to operate.

Distributed temperature sensing is a newly introduced technique capable of complex structural health monitoring systems. Temperature and pressure control is especially important for dams and tunnels with their difficult-to-access locations and other challenges that staff usually face. SHM is the solution for these situations.

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

FBG Sensors for Concrete Constructions

FBG sensors are used to monitor structures made of various materials, including concrete and metals. In particular, we are talking about structures that usually consist of metals such as aluminum, steel, copper, etc. Fiber Bragg Grating Sensors for Concrete Constructions

Concrete Constructions’ Main Issues

Reinforcement plays a major role in concrete structures. Its strength and durability can affect the appearance and growth of the cracks. One of the reasons for such a degradation is corrosion.

Corrosion occurs when a substance reacts with its surroundings, resulting in the material’s consumption or contamination by an environmental component. Corrosion can reduce the life and load-bearing capacity of a structure. Due to the chemical reactions caused by corrosion, it may change the reflection of the steel surface. The thicker the material, the more it will be subject to deformation. Here, structural health monitoring (SHM) delivers the results.

Structural Health Monitoring (SHM) is an important tool used to monitor the occurrence of corrosion. It is effectively used in constructions to detect and prevent any possible damage. Early corrosion monitoring is essential. Corrosion is dangerous because it causes high costs to repair, and it takes some time to be discovered. In the most extreme cases it can bring the collapse of the complete structure.

Types of Corrosion Monitoring Devices

Today, there are a number of inspection technologies that have been developed specifically for the purpose of detecting damage to constructions. These methods include acoustic emissions, ground penetrating radar systems, electromagnetic techniques, etc. However, they all have their shortcomings including susceptibility to electromagnetic disturbance and lack of continuous structural health monitoring.

Fiber optic sensors are an effective solution for structural health monitoring. They provide real-time monitoring and low-cost techniques that monitor and control the corrosion appearance. There are a variety of fiber optic solutions available such as fiber Bragg grating sensors, FBG interrogators, distributed sensing systems, etc.

Corrosion conditions may vary due to their structure. Therefore, there is a need for a great number of point sensors. This is where distributed fiber optic sensors really come into their own.

Fiber Optic Sensing for Structural Health Monitoring

FBG sensors are used as instruments for corrosion detection. Like any standard sensor, fiber optic sensors are built into the structure to collect all the data and transmit it to the unit. They directly or indirectly measure vibration, displacement, humidity, temperature and chemical changes. FBG sensors are divided into several types due to the parameters they measure: displacements, strain, temperature, etc. By displaying this data, they are able to predict the occurrence of corrosion and its future consequences.

Here is a list of the major features of the FBG sensors:

Portability;
High accuracy;
Simplicity;
Long life;
Easy to integrate;
Electromagnetic interference and corrosion resistance;
Ability to operate in harsh environments, etc.

FBG sensors are particularly indispensable for monitoring corrosion in the hidden areas that are usually inaccessible to specialists. Their compact size allows for high accuracy and resolution. However, fiber optic sensors do not detect corrosion appearance directly but by estimating the material layer deposited on an optical fiber. That’s why they should be located close to the structure, in the same conditions.

FBG sensors have shown promising future in interaction with the concrete structures. This expands the horizon of their applications, including critical facilities and civil engineering.

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Fiber Bragg Gratings for Civil and Geotechnical Engineering

Specialists have already found a series of applications where fiber Bragg gratings have shown to be profitable. FBG sensors have become a reliable distributed sensing solution for structural health monitoring. In addition to other applications, such as in the biomedical field, they are also used in civil engineering and geotechnical engineering.

All these areas have one thing in common – the environmental conditions. In such environments, it’s difficult to prevent the degradation processes such as aging and chemical effects. These factors should also be taken into account when implementing the traditional monitoring systems or equipment. In most cases, they have a short service life and require frequent replacement.

Alternatively, fiber optic sensors deliver modern fiber optic solutions that are able to work in extreme environments. FBGs for Civil and Geotechnical Engineering

Fiber Bragg Grating Sensors Common Characteristics

Since their first implementation, FBG sensors have been broadly deployed especially for distributed sensing of temperature, strain, and other characteristics that are particularly valuable in geotechnical and civil engineering. Fiber optic sensors have become world renowned for the features they offer. High sensitivity, immunity to electromagnetic interference are the most important parameters that are in demand.

Like traditional sensors, FBG interrogators face similar challenges. For example, they are usually required in extremely accurate equipment. That’s why there’s a high demand for maximum precision and high spectral resolution, down to picometer level. Fiber optic devices are also increasingly being used to deploy in rugged environments.

Fiber Bragg gratings are compact and can provide stable operation and durability in outdoor environments. For example, they are typically exposed to moisture influences, chemical reactions, temperature variations, etc. Distributed sensing systems should meet all the necessary requirements to ensure safety and proper operation of the entire system and to avoid the consequences of the interaction of the sensing element with the environment.

To ensure that, fiber optic systems should have robust materials and construction. In addition to complete, reliable fiber optic systems, fiber optic cables play a crucial role in creating the long-term FBG structural health monitoring systems. All fiber optic sensors should be able to withstand a certain level of thermal and mechanical loads at all times. The only way to provide customers with the best fiber optic solution is through testing of FBG sensors and application methods.

FBG Inscription Methods

Depending on the application and environmental conditions in which the FBGs are to be used, specialists can design FBG sensors for individual customer parameters.

A fiber Bragg grating is a fiber optic microstructure in which the index of refraction within the optical core changes along its length. The producing process of FBGs is usually called “writing”. Nowadays, there are three FBGs inscription methods:

The interferometric method is based on exposing a light sensitive area of the fiber to an interferometric fringe pattern to get the full grating. The pattern is achieved by illuminating an appropriate mask. In this case, the phase mask period defines the FBG period.
Continuous core-scanning method. Here, the FBG writing is provided by the motion of the translational frame where the fiber is fixed. In this technique, the period of the FBG is defined by the modulation frequency and the translation speed of the fiber.
And the last is the direct point-to-point method based on the absorption of a laser pulse. Each grating element is generated by controlling the laser parameters and moving the fiber. In this technique, the FBG period is determined by the fiber translation speed and the laser pulse repetition rate.

Applications of FBG Sensors

Fiber Bragg grating sensors are used in various fields where it is required to monitor structural health. In engineering, they are used to monitor the integrity of the entire structure and observe any deformation of its components. Such monitoring leads to the reduction of the risks and safety requirements. Fiber optic sensors are particularly useful for reinforced concrete structures because they can provide online data on the risk of corrosion.

When we talk about geotechnical and civil engineering, FBGs have also found their place for implementation.

Here are some examples of how fiber optic technology gets used:

Concrete structure monitoring;
Lateral deformation monitoring of embankment soft soil;
Pressure monitoring of tunnel’s rock and soil;
Structural health monitoring of bridges, dams, etc.

Nowadays, FBG sensors are also used to monitor landslides and slope failures and have shown good results. Distributed sensing systems have been applied to examine the landslide stability and deformation of landslides. Nevertheless, installing monitoring systems in complex environments and dealing with uncontrollable boundary conditions require careful consideration of potential issues.

Monitoring engineering and geotechnical structures with distributed sensing systems can improve profitability. Structural health monitoring methods are often preferred due to their ability to:

operate in chemically aggressive environments;
their feasibility in hard-to-reach areas of structures;
use fiber optic solutions which reduce equipment costs by utilizing a single fiber optic cable.

Overall, fiber Bragg gratings find extensive use in geotechnical and civil engineering applications. And, as with any technology, the successful implementation of fiber optic technology requires specialized experience and professionalism in designing and implementing the entire fiber optic system. Most of all, when there is a need for long-term measurements.

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Distributed Sensing for Seismic Monitoring Systems

We have already published a range of articles referring to different applications of fiber optic technology in various industries and fields. Geophysics has also applied distributed sensing as a powerful instrument for structural health monitoring, such in, the oil and gas industry, tunnel safety monitoring, etc.

Seismic monitoring has been no exception. Resistance to electromagnetic disturbance, cost-effectiveness and possibility of implementing into hard-to-reach regions or places that can be harmful for human health are undeniable advantages of distributed sensing systems. Distributed Sensing for Seismic Monitoring Systems

What is Distributed Sensing Technology?

Distributed sensing is a technology that provides continuous measurements in real-time. Compared to traditional sensors, placed at certain points, distributed sensing acts as a sensing element along its entire length because the whole fiber optic cable is applied.

Due to the exploitation of the entire fiber optic cable all over its length, this method is considered to be one of the most cost-effective tools that can be placed in severe conditions.

Operation Principle of the Distributed Sensing Systems

In simpler terms, DAS systems as a part of the distributed sensing technology consist of several components including fiber optic cable and an attached optoelectronic device – FBG interrogator. The interrogator sends short pulses of the pulsed laser light into fiber optic cable. Then the backscattered light moves back up the fiber to the FBG interrogation unit. Due to the time that the laser pulse takes, there can be found the relation backscatter event and a fiber distance.

The FBG interrogator is connected to a processing unit that processes and stores the received data. This unit gets the raw data and transfers it into the information that is displayed in the program.

The software provides the visualized analysis that includes the previous data as well. In case there are any differences, fiber optic system alarms specialists. For instance, the system can display the location of the fiber optic cable on the map and highlight locations where the rates have changed or exceeded acceptable limits.

What’s the Difference Between DAS and DTS Systems?

Traditionally, distributed sensing systems are divided into distributed temperature sensing and distributed acoustic sensing.

The main difference between DTS and DAS systems is the type of signals they get to provide analysis. DTS systems are sensitive to temperature changes, while DAS is sensitive to acoustic vibrations. Therefore, their operation principle is also different. Due to the fiber qualities, the performance of DTS systems is able to stay at the necessary high injected pump power level. At the same time, DAS systems don’t require such high pump power as DTS systems because of the Rayleigh scattering.

DAS Systems and Their Applications in Seismic Monitoring

If we are talking about seismic monitoring, distributed acoustic sensing is used. DAS systems measure any vibrations that can’t be detected by DTS technology.

The goal of all seismic monitoring systems is warning before any accident occurs. Their effectiveness depends on the accuracy of the obtained data, lifetime and length. That’s why there is a necessity in a continuous operating system that is capable of working in severe environments and over long distances.

DAS systems were implemented as seismic monitoring systems due to the above-mentioned advantages as well as low cost, no special maintenance, robustness, etc. Therefore, distributed acoustic systems have provided new capabilities for seismic monitoring.

Field Projects Where Sensing Systems Were Applied

If we are talking about sensing systems, in most cases fiber optic sensors were more effective in comparison with the conventional electronic ones. That provides unrivaled performance, especially in critical applications.

For example, two years ago the specialists started a range of experiments in the Arctic and the Arctic Ocean. This is the first case when DAS systems were installed in the Arctic. Scientists wanted to get the analysis of the seafloor seismic activities and other processes under Arctic sea ice with a distributed acoustic sensing system. Fiber optic cable catches the vibrations about all the changes of the ocean 24/7.

The other project with DAS systems has also allowed scientists to see them in other severe environmental conditions. Since they are installed mostly in the ground, specialists have monitored their performance in snow. The most concerning parameters for them were the snow depth and severe frosts.

Finally, in the conditions of decreasing temperatures the reduction in background noise and better signal-to-noise ratio was noticed. In fact, the lower temperatures, the better results distributed acoustic sensing has provided. Cold temperatures don’t make fiber optic performance difficult or interfere with accuracy of the received data. Moreover, fiber optic cable is able to transfer signals at snow depths of at least 0.65m.

Distributed sensing as a tool for seismic monitoring systems has proved to be effective in detection of any seismic shocks and flow changes. All in all, DAS provides capabilities for seismic monitoring of the near surface.

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FBG Interrogators and Other Fiber Optic Technologies

Fiber optic technology has become a solution that takes its place in many processes due to its benefits and stable performance it provides. It contains a wide range of tools such as fiber Bragg grating sensors, FBG interrogator, etc. All equipment contributes to distributed sensing and plays its own different role. FBG Interrogators and Other Fiber Optic Technologies

FBG Technology Principle

Fiber Bragg grating is a microstructure. It might be integrated into the optical fiber’s core. FBG is usually approximately a few millimeters in length. The interference pattern in the core is done with the help of the UV laser beam and a phase mask.

According to the technology, the index of reflection changes along the length in the fiber core. Its modulation makes a fiber Bragg grating play as a selective mirror that is able to reflect certain wavelengths and transmit the others. The light that continues to pass through the optical fiber to the following fiber Bragg grating travels without any loss. The reflected wavelength is defined by the microstructure interval and the index of refraction of the core.

The FBG system contains two main elements: FBG interrogator and a range of fiber Bragg grating sensors.

FBG Interrogators

FBG interrogators are optoelectronic units playing a role of measurement and data collection systems. FBG interrogator is an important part of the distributed monitoring system that enables instant figures of fiber Bragg grating (FBG) sensors and data transmission.

An FBG interrogator is able to provide data from the network of sensors. Fiber optic sensors can be presented by different types of sensors that measure different parameters, for example, temperature, strain, displacement, etc. They are connected into one distributed monitoring system that acquires information simultaneously.

During the data acquisition, FBG interrogator acts as a radar, sending pulses into the fiber and getting the signals back. The interrogator registers the received wavelengths and then transfers them into engineering units. With highly accurate FBG interrogators, fiber optic sensing systems are able to provide reliable data over a wide distance. FBG interrogators efficiently provide precise measured data twenty-four hours a day using computer software. Due to the software, data can be stored and later analyzed.

Fiber Bragg Grating Sensors

The other element of every sensing system, except for FBG interrogator, is fiber Bragg grating sensors. FBG sensors are sensors based on the same principle of fiber optic technology. They usually present a chain of sensors creating a single optical fiber. This chain commonly consists of up to 30 fiber Bragg grating sensors per fiber.

Fiber optic sensors proved to be the best solution compared to traditional electrical sensors. They have proven to be highly accurate, relatively simple instruments capable of operating in severe environments. In contrast with conventional electrical sensors, fiber Bragg grating sensors are immune to electromagnetic influences (EMI) and mechanical fatigue.

The diversity of FBG sensors is quite wide. The most common types of sensors are:

Temperature sensors;
Strain sensors;
Displacement sensors;
Pressure sensors, etc.

Fiber optic sensors can be implemented in different field projects. Depending on the purposes, multiple fiber optic sensors or array of sensors can be installed. They are able to take measurements for one or several parameters in different places. The FBG sensors can be embedded into the structures or surface mounted.

FBG systems that contain fiber Bragg grating sensors and FBG interrogators have found their applications in many areas. They are proven to help in development and monitoring of different constructions, vessels, systems, etc. Fiber optic technology has proven to be cost-effective and efficient.

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Fiber Optic Sensor (FOS) Technology and its Applications

Thanks to all the advantages of the fiber optic sensor (FOS) technology and its diversity of instruments, described in the previous article, there are a range of applications. Structural health monitoring of the concrete constructions is proved to be the most effective tool for management of the infrastructure, due to the latest results. FOS Technology and its Applications

Here is a list of the most common applications where fiber Bragg grating sensors can be installed.

Bridges

The lifetime of every large bridge is several decades or hundreds of years, including the period of construction and repair stages. Despite the improved quality of the bridges’ planning, it is still difficult to accurately predict its lifetime because of the complex structures and external influence like corrosion or the natural disasters like earthquake, flood, etc.

The structural health monitoring in real time gives an insurance of the safety of bridges. According to the researchers, this fiber optic system can be applied on the different stages of the bridge construction. Most of all, these fiber optic monitoring systems are used in the operation or safety phase of bridges and extend their lifespan.

The FBG structural health monitoring systems include fiber optic sensors, multiplexers, FBG interrogators, local and remote computers.

All in all, the fiber optic monitoring systems provide the following advantages:

Control of state of metal structures;
Control of the bridge oscillation frequency;
Notifications for the personnel on screen;
Extending the bridge’s lifetime, etc.

Moreover, when we talk about the railroad bridges, it is also possible to evaluate the lower bridge beam condition.

Buildings

The state of the load-bearing structure and building foundation is a crucial element of safety. And fiber optic sensors have made a great contribution to it.

The structural health monitoring can be applied whether for the buildings under construction or for the old houses when there is a severe level of damage and degradation of materials. Unfortunately, the majority of the houses that were built before, mostly in the previous century, are particularly vulnerable to environmental actions. Basically, because there was no specific constructive detailing that would provide the age resistance of the constructions.

The degradation usually includes steel corrosion, debonding of concrete, etc. It becomes visible when the damage is greatly extended on the elements of the structure. If the moment for the structural repair is missed, it often leads to its more complex and expensive modernization. At worst, there is a need for demolition.

Mostly, fiber optic technology is used for:

Control of the strain-stress state of metal basic structures and foundations;
Monitoring of the cracks and foundation shrinkage in reinforced concrete structures;
Snow load control.

Tunnels

The structural health monitoring systems have also made a great contribution into tunnel construction.

The most important safety factor in tunnels, as in many civil structures, is the deformations. Fiber optic sensors can monitor and provide the useful data both within the construction phases and over the long term. In the long term, monitoring calls a very stable and precise system that can compare deformation measurements over long periods. In the short term, the monitoring system can measure deformations that occur for relatively short periods.

The structural health monitoring system influences the tunnels’ management and security by providing in-time maintenance and restoration. There is a problem of excessive deformations which can seldom affect the structural security, but can cause durability problems.

For example, such fiber optic monitoring systems can be applied during the highway tunnel’ construction to measure the tunnel load or to monitor railway tunnels. Besides, the knowledge of the tunnel’s behavior helps while the introduction of the modern building techniques or for the prolongation of its service life in the future.

Hydroelectric and Wind Power Plants

Fiber optic solutions have found their applications for nuclear, hydroelectric, wind power plants. Aging management of the components is directly related to their operation. Safety requirements guarantee their safe operation but still are difficult for operators to track fully. All kinds of power plants require the accurate and qualified assessment of the thermomechanical loads and other parameters that can lead to the early aging of the equipment.

Fiber optic sensing is one of the best monitoring and maintaining systems for the plants. Structural health monitoring (SHM) of hydroelectric plants, wind turbines and others gives operators real-time information of the components’ condition.

Dams

As for the dams, fiber optic technology helps in detection of the seepage flow changes in a dam structure. Dams usually face different problems connected to external loads such as water level changes, seismic disturbances, etc. Any changes in numbers can be a sign of erosion which is the most common cause of the dam failure.

Fiber optic system allows operators to get the data from all over the dam as measurements are taken along the full length of the cable. Distributed sensing detects the tiniest changes in rates that otherwise can lead to the operational failures.

Fiber optic sensors are able to measure various parameters and quantities in structural health monitoring. Depending on the required operating principles, specialists discuss which type of FBG sensor is the best suitable and their way of embedding and surface mounting. All in all, their final goal is to find the most effective fiber optic solution for the operating principle and potential applications in SHM.

The short list of applications can be also found on our website.

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

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Fiber Optic Technology as pipeline leak detection method

Fiber Optic Technology for the pipeline leak detection Special fiber optic technology can make fiber optic cable a sensing one. That solves many challenges including monitoring long units like pipelines, tunnels, or power cables. With the help of fiber optic sensors, it is more likely to find the leak in a short time. FBG interrogator sends a laser pulse through the fiber optic cable and the light comes back to the interrogator. The back scattered light delivers back acoustic, vibration, and thermal data.

Distributed sensing is widely used as an external pipeline leak detection method. Distributed sensing systems easily detect changes in temperature, noise, or vibration. Distributed sensing helps in detecting internal events, for example, liquid accumulations in gas pipelines, slugs, and flow constrictions.

Nowadays, distributed sensing pipeline leak detection software includes a wide variety of pipeline applications. The systems that apply distributed acoustic sensing (DAS) or distributed temperature sensing (DTS) are already produced in many projects across tens of thousands of kilometers of pipelines. Therefore distributed sensing systems already proved to be the most cost-effective in leak detecting.

There are standard fiber optic cables with suitable distributed sensing systems compatible with single-mode and multi-mode fibers or with a combination of them. According to the scientists, fiber optic cables with the usage of single-mode fibers are suitable for both DAS and DTS. While fiber optic cables using multi-mode fibers could enhance the DTS systems’ performance. Distributed sensing systems emphasize the detection of thermal and acoustic leak signatures. That’s why there are different types of DAS and DTS systems according to their thermal, acoustic detection capabilities, and performance requirements.

For example, a research team from South Africa is currently applying fiber optic solutions for the detection of leaks in pipelines. Scientists investigated leak detection using fiber Bragg gratings. These were applied to measure strains and temperature on pipelines and in the ground adjacent to pipelines. With the help of fiber optic technology, they could detect water leaks by burying a fiber optic cable into a pipe trench with a new pipe or place it above an existing pipe.

The scientists hope that after a number of experiments they could implement distributed sensing systems in South Africa by monitoring the pipes and delivering the data about water leaks into a leakage detection center. So fiber optic solutions would give an opportunity to fix the leak quickly without losing massive volumes of water. According to them, fiber optic technology shows great promise as a highly effective leak detection system.

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Low-cost FBG interrogator for dynamic measurements

FBG interrogator for dynamic measurements Fiber Bragg grating technology (FBG technology) offers fiber optic sensors that allow carrying out the measurement of such parameters like temperature and/or mechanical strain. However, the high cost of fiber sensing systems is considered to be a major disadvantage for commercial applications.

It should be noted that the popularity and fast growth of fiber optic technology for sensing applications promote numerous research in various areas, for example, industry, medicine, aerospace, civil applications where such physical and chemicals factors as acceleration, level, temperature, strain, pressure, deformation, refractive index play a very important role.

Optical fiber sensors are perfect for use in the mentioned measurements. Fiber optic technology offers numerous benefits that include “intrinsic safety, resistance to chemical corrosion, immunity to electromagnetic interference, electric isolation, compact size, lightweight sensing heads, high resolution, easy multiplexing, and capability for extremely remote monitoring without the need of electrical power at the measuring point”.

Moreover, fiber Bragg gratings are the most used technology for the measurement of temperature and/or mechanical strain parameters among other optical fiber sensors. To be more precise, the term “fiber Bragg gratings defines as nanometer periodical refractive index changes engraved in an optical ﬁber core.”

The principle of FBG technology operation is based on the injection of a broadband light spectrum in the optical fiber. Herewith, there is a concentration of the reflected spectrum at the fiber Bragg grating wavelength, herewith, it is possible to see a suppression in the transmitted signal at the same wavelength.

Additionally, the same operation principle of the FBG technology is used in new and more complex structures, for example, planar FBG sensors. Thus, the FBGs offer very precise measurements due to the wavelength that is considered to be a permanent feature of the signal along the optical fibers.

Nevertheless, the FBG interrogators have some challenges in large commercial applications because of their high cost. That is why the development of new, low-cost alternatives to the current FBG interrogators is highly required. Therefore, there are several solutions to the present problem.

One of the solutions is the use of frequency-to-amplitude conversion (a fast and low-cost FBG interrogation technology), in which the spectral variations of fiber Bragg gratings are straightforwardly transmitted into optical power variations. Herewith, the presented FBG technology is based on the twist between both the FBG sensors and the edge filter spectra.

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

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DTS system controls oil rim movement

DTS for oil rim detection Today operators in highly fractured carbonate reservoirs use running wireline gradiometric surveys as a traditional way of oil-rim movement monitoring. Nevertheless, the method is not ideal because it does not allow providing the necessary information in a manner timely enough to influence operations since the surveys are conducted just a few times a year. Distributed temperature sensing (DTS) system is an alternative solution that overcomes these drawbacks.

Distributed temperature sensing offers real-time monitoring of the oil rim in carbonate reservoirs. DTS technology is based on the use of optical-fiber Bragg gratings (FBGs) and is able to measure pressure in extreme environmental conditions. It should be noted that the DTS system does not require electronics, herewith it provides long service term even at elevated downhole temperatures. Also, distributed temperature sensing is quite stable, it can determine even small pressure changes.

Moreover, dozens of distributed temperature sensors can be implemented on one fiber optic cable connected to the FBG interrogator. The principle of operation includes a diaphragm pressure transducer that converts changes in the hydrostatic pressure of its environment into the deformation of a pressure-sensitive diaphragm, and then into the strain, within an optical fiber attached to the diaphragm. The thing is that optical fibers offer numerous advantages for oil and gas industry application, containing the following:

high transmission efficiency that means the FBG interrogator can be installed several kilometers away from the downhole sensors;
high data quality and accuracy due to data encoding in the light wavelength;
data immunity to the electromagnetic influence by machines;

At present time the information about pressure and temperature measurements, as well as system-health and self-diagnostic information are transmitted from the FBG interrogator into a database at 3-hour intervals. If fresh data sets are obtained, an algorithm processes them into gas/oil-contact and oil/water-contact locations. Also, it is possible to visualize pressure, temperature, and fluid-level data to see them in real-time.

Further improvement of the DTS system will allow the application of the system for the production monitoring in ultrahigh-temperature thermal-recovery wells, where fluid temperatures up to 280 °C can be reached. Finally, distributed temperature sensing provides the reduction of a production delay, the reduction of operational costs, health, safety, and environmental risk reduction, and the possibility of system expansion.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating 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 temperature measurement systems and want to learn more, please contact us at info@optromix.com

DTS system FBG interrogators FBG temperature sensors

Fiber Optic Sensing: Fiber Bragg Grating Sensor Interrogation Systems

FBG sensor interrogator systems can be deployed into a variety of fields. These products feature high reliability, advanced command and data output control, and incredible speed and sensing range.

Fiber Bragg grating (FBG) sensors have been well known and widely used for around 20 years for the following reasons: they are light, compact, easy to install, require very low maintenance, can be used in highly explosive atmospheres, and are immune to electromagnetic interference. Fiber optic sensors have a wide range of possible applications, which include temperature sensing, strain and bending measurements, medium refractive index measurement.

Despite numerous advantages of fiber optic sensors, it is important to install an FBG interrogator to retrieve accurate data and measurements from the sensors. Here is the main principle of how the fiber optic interrogator works: after the light has been sent into the fiber and has been reflected from the FBG, it travels to the interrogator – it’s photodetectors – which then compares it to the wavelength reference artifacts; after that, the interrogator determines the position of the FBG center wavelength. This information is later converted to some measurement units.

There are multiple types of FBG interrogators; each type offers different advantages over others, for example, the number of optical channels and Wavelength range. For example, high-frequency FBG interrogators provide an opportunity to work with dozens of fiber optic sensors at high speed. This characteristic also provides an opportunity to use multiple fiber optic interrogators at once.

The wavelength range of the FBG interrogator plays an important role when it comes to how many wavelengths or bandwidth information from an FBG sensor it can process. Some FBG interrogators have a very limited wavelength range, only around a few nm, however, this is not ideal for most FBG systems. The broad wavelength range of the interrogator provides better measurements.

Another important characteristic of FBG interrogator is the number of optical channels. Each channel represents an optical line, therefore, the bigger the number of optical channels, the more optic lines the interrogator can handle at once. Most interrogators have one optical channel and dedicated to one particular optic line.

Other approaches to FBG sensor interrogating, some of which include:

Broadband source, Dispersive element, Diode Array;

This method is less reliable than the aforementioned ones due to limited resolution, which is a result of the inherent limitations of commercially available diodes.

2.Broadband source, Optical Spectrum Analyzer/Multi-line wavelength meter;

optical spectrum analyzers are large and expensive, which makes them less desirable in a laboratory setting. They are also not able to perform optimally under some temperatures.

3.OTDR/TDM systems;

The system cannot handle a large number of sensors on the fiber as its data acquisition rates scale down with increasing sensor counts.

4.External Cavity Tunable Laser, Power Meter, Wavelength Meter;

External cavity tunable lasers have low speed and do not have a wide operating temperature range. Moreover, they are expensive and do not have the required mechanical robustness.

Optromix interrogators can control up to 8 optical channels. The interrogator operates with the 20 maximum sensors per channel. The device is controlled by the PC with the specialized software for sensors monitoring. The system contains a broadband source of radiation and it can carry out spectrum analysis.

Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Optromix, Inc. is a top choice among the manufacturers of fiber optic devices.

If you have any questions, please contact us at info@optromix.com

FBG interrogators fiber Bragg gratings fiber optic sensors