Optical fiber temperature sensors and their applications

FBG temperature sensorsFBG sensors give the opportunity to measure a variety of parameters in conditions where other sensor technologies fail or simply cannot operate. Such FBG sensors have intrinsic advantages, including resistance to electromagnetic interference, non-electrical conductivity, passive measurements, small size and small weight, and the option of multipoint measurements. the reflection wavelength of the FBG (Bragg wavelength) depends on the grating characteristics (period, modulation) and is influenced by the ambient conditions such as strain and temperature. The development of fiber optic devices based on fiber optic sensors for operation in harsh environments (such as for temperatures of up to 1000°С) is becoming an increasingly important field. In the case of temperature sensing the Bragg wavelength is a function of the temperature. This temperature dependence results from changes in the refractive index of the fiber as well as from thermal expansion of the glass material. Many material properties show strong temperature dependence. Examples of such temperature dependencies are dew point, density, electrical conductivity, refractive index, rigidity, and diffusion. Temperature measurement also plays an important role in the health monitoring of electric circuits or civil structures.

The main advantages of FBG sensors are their measurement of reflected light, wavelength-encoded sensing, and multiplexing capability. Nowadays there are many types of FBG sensors used for measuring temperature: intrinsic and extrinsic.

Three major types exist:

  • The intensity-modulated sensors

Intensity-modulated FBG sensors are based on the principle of letting a physical disturbance such as temperature cause a change in the received light through an optical fiber;

  • The phase-modulated sensors

The phase-modulated FBG sensors are based on the principle of comparing the phase of light in the sensing fiber with a reference fiber in an interferometer;

  • The wavelength modulated sensors

Wavelength modulated FBG sensors are based on the principle that a physical disturbance such as temperature or strain changes the reflected wavelength of the light.

In general, it should be noted, phase modulated and wave modulated FBG sensors are providing much more accurate measurements than intensity-modulated sensors but at the cost of much more expensive interrogators.

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 Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

Fiber Optic Products for Aircraft Structural Health Monitoring

FBGs for aircraft health monitoringAircraft structures require regular, scheduled inspections and monitoring of all possible hazards due to their special conditions and the principles of their design. Therefore, structural health monitoring is conducted through fiber optic devices and has great potential to reduce the costs related to these operations. Fiber optic devices applied to the monitoring of aircraft structures provide some advantages over traditional devices. Fiber Bragg grating sensors have proved to constitute the most promising technology in this field. In order to prolong the operation period of all kinds of complex engineering systems and avoid catastrophic failures, so it is necessary to achieve the highest levels of damage detection. The automation of the inspection process is a point of major importance to reduce inspection efforts. The structural health monitoring system on the basis of fiber optic products can be defined as a set of devices that provide information that allows us to locate, evaluate, and predict the loading and damage conditions of a structure. The structural health monitoring of aircraft structures can conduct real-time checks, reducing costs, and improving the reliability and performance of the structures. A wide range of potential structural health monitoring technologies is being developed to meet these needs, and the most promising options are:

  • electrical strain gauges and crack wires
  • acoustic emissions methods
  • optical-based technologies
  • comparative vacuum monitoring
  • microelectromechanical systems (MEMS)

Fiber optic products and fiber optic devices, in general, are very appropriate to perform structural health monitoring due to the fact that they have their intrinsic capabilities, such as sensitivity to electromagnetic radiation, low weight, compact size, great sensitivity and resolution, and their suitability to be embedded into structures. Fiber optic devices for monitoring the strain in aircraft structures can be classified into the following categories: intensity-based, interferometric, distributed, and grating-based fiber optic devices.

Among grating-based sensors, FBGs and probably the most mature and widely employed optical sensors for structural health monitoring of engineering structures due to their fast development achieved in recent years. Fiber Bragg grating sensors have important advantages over conventional strain sensors:

  • high sensitivity and resolution, low weight and small size, the absence of the electromagnetic interference
  • suitability for being attached to a structure or embedded in composite materials
  • high multiplexing capability
  • wavelength-encoded sensing in a way that is totally independent of the optical intensity
  • different magnitudes can be measured using FBGs, such as strain, temperature, vibration, or humidity.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line: fiber Bragg grating sensors, FBG interrogators, and multiplexers, Distributed Temperature Sensing (DTS) systems. We create and supply a broad variety of top-notch fiber optic solutions for the monitoring of various facilities all over the world.

If you are interested in Optromix FBG sensors, please contact us at info@optromix.com

Fiber Bragg grating strain sensors for structural health monitoring

Fiber Bragg gratings stand out among other fiber optic sensors as the most developed and prominent technology for the measurement of strain, vibrations, temperature, and pressure. FBG sensors have attracted significant interest in structural health monitoring due to numerous advantageous properties:

  1.  immunity to electromagnetic interference;
  2. intrinsic fire safety;
  3. low invasiveness;
  4. minimum aesthetic impact;
  5. possibility to send the data remotely using the same sensing fiber.

There are multiple sensing advantages that FBG sensors provide. First of all, FBG sensors perform with an excellent balance between complexity and performance, which is one of the most attractive qualities of fiber Bragg grating sensors for structural health monitoring. Secondly, FBG sensors are able to work in low signal-to-noise ratios better than other optic sensors. Moreover, fiber Bragg grating sensors are predictable and less dependent on the temperature of the surrounding environment, as well as are well-suited for multiplexed optical sensor networks.

Over the past decade, structural health monitoring has attracted a lot of attention as modern technology develops, and new materials and compounds are used in the construction of buildings and structures. Structural health monitoring involves the collection and analysis of information obtained through measurements of the structure. The results of data analysis are used to assess the damage and evaluate the performance of the structure under harsh conditions.

FBG sensor structural health monitoring has become an important tool for assessing the performance of different structures and measurements of temperature, strain, pressure, displacement, etc.

Fiber optic strain gauge is welded directly to the surface of the metal structure (pipes, beams, etc.), and it has a protective silicone cover. Fiber optic strain sensors are durable and stable, widely used for civil engineering constructions, particularly they reinforce concrete structures exceptionally well.

Fiber Bragg Grating strain sensors demonstrate lots of advantages compared to the regular electrical strain gauges. Namely, they are immune to electromagnetic interference and power shortages. Compact size devices provide the most accurate measurements. FBGs are, literally, the best strain sensors right now.

If you would like to purchase Optromix FBG Strain Sensors, please contact us: info@optromix.com or +1 617 558 9858

Fiber Bragg grating sensor systems in structural health monitoring

FBG sensors for structural health monitoringA traditional way of monitoring structural health is through the use of piezoelectric transducers; these devices convert pressure to an electric voltage. Transducers are reliable and accurate in most working conditions except in cases of corrosive environments or under high temperatures, above 300° Celsius. Harsh conditions influence reliability.  accuracy, and usefulness of transducers in a negative way.

A new solution for structural health monitoring has been developed to accommodate the needs of the industry. Fiber-optic based technology, like fiber Bragg grating sensors, are more reliable under harsh conditions such as high temperatures and corrosive environments; they are immune to electromagnetic interference that is detrimental to piezoelectric transducers’ operation. FBG sensors are designed to operate under harsh conditions and provide reliable data. Fiber Bragg grating sensors are able to measure a variety of factors, such as temperature, strain, pressure, the appearance of cracks, etc.

The reliability of FBG sensors for structural health monitoring is ensured by the simplicity of the optical fiber material—fused silica—that forms the fiber. FBG strain sensors and FBG pressure sensors are especially useful in monitoring the condition of critical infrastructures operating under harsh environments, such as modern superheaters or nuclear power plants, thus ensuring the continuous operation of power plants, preventing catastrophic consequences of structural failures.

One of the applications of FBG sensors is the monitoring of the P91 pipes widely used in the industry. These pipes transmit high-pressure steam, which is both high-temperature and corrosive. Fiber Bragg grating temperature sensors indicate overheated pipes that may be under too much stress. FBG pressure sensors are used to detect critical increases in pressure within pipes to prevent premature breakdown of the systems.

One of the advantages of fiber Bragg grating sensing systems is its cost-effectiveness. FBG sensors’ price is low compared to other methods of temperature, strain, and pressure measurements.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line: fiber Bragg grating sensors, FBG interrogators, and multiplexers, Distributed Temperature Sensing (DTS) systems. We create and supply a broad variety of top-notch fiber optic solutions for the monitoring of various facilities all over the world.

If you are interested in Optromix FBG sensors, please contact us at info@optromix.com

Crack monitoring of wind turbine foundations using FBG strain sensors

FBG strain sensors for crack monitoringThe increased demand for energy due to the growing population has forced the industry to develop new sustainable ways to produce energy. Among new and developing energy technologies are wind turbines. They are widely used to produce energy in many parts of the world. However, there are multiple concerns that are yet to be solved, one of them has been the lack of effective monitoring devices and techniques. Structural health monitoring of wind turbines is needed to ensure that the infrastructure around wind power remains reliable. It is crucial to monitor the operation of wind turbines to ensure effective wind power generation and avoid costly downtimes.

Besides monitoring of wind turbine temperatures, which can be effectively performed with the use of FBG temperature sensors, the monitoring of wind turbine foundations can prevent premature decay of the foundations and prolong the operational time of the turbines. Often the access to the underground part of the foundations is limited, therefore the degradation of onshore, reinforced-concrete wind turbine foundations is assessed via above-ground inspections, or through excavations that suspend energy generation. Sustained measurements of crack behavior could be used to quantify the risk of water ingress and reinforcement corrosion. However, the cracks that occur during turbine operation are not monitored. A solution to this issue is the use of fiber Bragg grating sensors.

Subterranean fiber Bragg grating strain sensors can be used to monitor the opening and lateral displacements of foundation cracks during wind turbine operation. Cracks that occur in the foundation of the turbines are often caused by the vibrations that are produced by turbines themselves. Therefore crack displacement results that are obtained via FBG strain sensors installed on the foundations are correlated with the strains measured by the second series of FBG sensors affixed to the turbine tower and verified against wind speed and turbine data from the operator.

The use of FBG strain sensors can be used to better assess the risks of water ingress and subsequent corrosion of the foundation’s steel reinforcement. The data obtained by fiber Bragg grating sensors may help engineers to more accurately determine the current asset lifetime and the design and construction of foundations in the future.

Fiber Bragg grating strain sensors demonstrate lots of advantages compared to the regular electrical strain gauges. Namely, they are immune to electromagnetic interference and power shortages. Compact size devices provide the most accurate measurements. FBGs are, literally, the best strain sensors right now.

If you would like to purchase Optromix FBG Strain Sensors, please contact us: info@optromix.com or +1 617 558 9858

FBG strain sensors in structural health monitoring

Fiber Bragg grating sensors are used over conventional sensors in structural health monitoring based on a number of advantages they provide:

  • FBG sensors are more stable;
  • fiber Bragg grating sensors are more durable, namely, they don’t rust;
  • FBG sensors can be highly multiplexed;
  • the sensors can be used in highly explosive atmospheres, like natural gas or oil.

These features are desirable for the health monitoring of complex structures. FBG structural health monitoring systems are essential in the design of smart buildings. The FBG sensor systems help to ensure building safety and performance. The systems are of particular use for buildings situated in earthquake-prone zones.

The mechanism behind FBG sensors allows to monitor complex structures based on the measurements of the wavelength of the reflected light; its wavelength changes under the influence of pressure, building incline, etc. Due to the fact that a single FBG sensor reflects a narrow region of the light, it is possible to multiplex them, which provides higher data accuracy. However, the number of FBG elements should be carefully designed and spaced in accordance with the range and bandwidth of the input light source.

The FBG strain sensors are fragile on their own, therefore they need to be placed on a base of some kind to protect them from outside physical influence. Usually, the sensors have a metal protective cover that prevents damage to the sensors from environmental factors. The sensors are then welded or glued to a structural member. FBG strain sensors, or FBG deformation strain sensors, can be used in both steel and concrete structures; they offer high accuracy and resolution. The measurements received from the sensors are often used to detect the behavior of structural materials under different environmental influences. The detection of segments that are stressed is essential for proper maintenance of the building and its structural parts and prevents premature aging and failure of these structures.

FBG strain sensors may also be used in the monitoring of tunnel ribs, pipelines, ship hulls, etc. Their high accuracy, easy installation, and compact nature provide a wide area of applications.

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. If you would like to purchase Optromix FBG Strain Sensors, please contact us: info@optromix.com or +1 617 558 98 58

Fiber optic sensor (FOS) technologies based on situ strain and temperature monitoring for tunnel structures

FBG sensorss for tunnel structuresNowadays, numerous civil infrastructures have been built in metropolitan areas all over the world. The performance of these infrastructures during construction, operation, maintenance, and upgrading is a major concern for society. The use of smart sensing technologies for structural health monitoring has attracted much attention due to their exceptional benefits. These technologies have developed rapidly and some have found widespread applications in civil and geotechnical engineering practices, such as fiber optic sensing (FOS), time-domain reflectometry (TDR) and etc.

Based on fiber optic sensor technology, a quasi-distributed fiber optic sensing array can be established to perform accurate strain and temperature measurements. Besides FBG, another popular FOS technology is the fully distributed Brillouin optical time-domain reflectometry (BOTDR), which enables the measurement of strain and temperature profiles along with single-mode optical fiber.

Compared with electrical strain gauges, fiber Bragg grating (FBG) sensing technology is a relatively novel method for tunnel structural health monitoring, which has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In order to study the internal force of the tunnel liner and detect the potential safety hazards, series of strain monitoring tests of a tunnel, taking into account the complex stress and strain variation during tunneling, were performed by employing the tandem linear FBG sensor arrays controlled by the wavelength division multiplexing (WDM) technology.

The length of the fiber, as well as the installation position of FBG sensors, depends on the size of the tunnel cross-section. For each test section, two layout methods could be employed: only using an independent fiber for the connection and signal transmission, or using two independent fibers according to the left and right sides of the tunnel cross-section.

 

BG sensors-based in situ monitoring on the internal force of the tunnel structure is of great environmental adaptability and performance stability. However, considering the cross effects of uncertain factors, such as special engineering properties, hydration heat of cement, and shrinkage and creep of concrete, the strain, and temperature collected through FBG sensors is influenced by composite factors. The stress and strain of liner concrete under the independent action of various factors cannot be analyzed accurately by using current ways. Therefore, it is necessary to conduct relevant studies to solve cross effect problems.

Optromix provides industry sensing solutions for Structural Health Monitoring (SHM) for different types of facilities. Optromix Company also offers a wide range of fiber optic temperature sensors for monitoring tunnel structures.  To learn more about SHM please contact us: info@optromix.com or +1 617 558 98 58

 

FBG structural health monitoring

FBG has been considered as an excellent sensor element, which is currently receiving more and more research interest. In order to measure strain/temperature variations with high accuracy, the ability to detect small shifts in Bragg wavelength becomes an essential requirement for an FBG sensing system.

With the construction of high buildings and bridges, etc., in recent years, the importance of structural health monitoring technologies to assess building safety is being re-examined. In previous systems using electrical strain sensors, every sensor required power supply, and the installed sensors were easily affected by electromagnetic noise, thunderstorms, etc., causing noise components in the electrical signal measured by remote sensing and presenting a risk of degraded accuracy. Optical fibers have been used as sensors to solve these problems with a focus on optical sensing technology. Since optical sensing technology does not require supplying power to the sensor itself, it offers many advantages including long life spans with excellent corrosion resistance, excellent explosion-proofs, easy remote measurement at distances of more than 10 km with no concerns about electromagnetic noise effects, etc. In addition, the characteristics of optical fibers lend them to linear and sheet designs for extreme environments, making them ideal for disaster monitoring and structural health monitoring systems.

Some of the well-known technologies in optical fiber sensing rely on measuring changes in the frequency of Brillouin backscatter occurring in optical fibers to determine structural deformations and temperature changes. Another method uses a Fiber Bragg Grating (FBG) forming a diffraction grating at the optical fiber core as a sensor to measure changes in the center wavelength of the optical spectrum reflected from the FBG sensor as an index of the amount of strain impressed on the fiber and temperature changes.  Since FBG sensor monitors are used mainly for natural disaster and structural health monitoring they are designed to be convenient for installation, small, and lightweight. Additionally, to be able to measure small strain and temperature changes quickly, they require a high responsivity of better than 1 kHz as well as better measurement accuracy than commercially available FBG sensor monitors and our previously developed model.