Distributed sensors for structural health monitoring of bridges and dams

FBG sensors for bridge monitoringNowadays distributed fiber optic sensors remain a subject of great interest for constant structural health monitoring of huge structures, for instance, bridges or dams. Herewith, the more sensing points there are, the more effective monitoring the sensing system offers. Thus, newly improved distributed sensors with 1 million sensing points provide prominently faster detection of structural problems that are now accessible.

Fiber optic sensors allow accurately detecting of erosion or cracking before a dam fails. Therefore, earlier detection of a problem by fiber optic sensing systems may lead to its possible prevention from later deformation or provision of sufficient time for evacuation procedures. Fiber sensors are considered to be perfect for controlling infrastructure since they suit for use in harsh environmental conditions and in areas that lack nearby power supply.

The operating principle of distributed sensors is based on “changes in the structure at any of the sensing points along with the optical fiber that causes detectable changes in the light traveling down the fiber”. Despite the high popularity of distributed fiber optic sensors, the main applications of sensors include the detection of leaks in oil pipes and structural health monitoring for landslides along railroads.

It should be noted that the novel fiber optic sensing system enables tracing train and temperature changes from 1 million sensing points over a 10-kilometer optical fiber in less than 20 minutes, while the strain parameter demonstrates deformation or mechanical stress on an object of interest. Herewith, the new distributed sensor is regarded as to be about 4.5 times faster than previous fiber sensors with 1 million sensing points. A larger number of sensing points require fewer optical fiber units for structural health monitoring of an entire structure resulting in cost reduction.

A large density of sensing points makes distributed fiber optic sensors suitable for such applications as avionics and aerospace, where every inch of a plane wing has to be controlled properly. According to researchers, the conventional technique of generating the continuous signal in fiber sensors undertakes distortions in the fiber optic system at higher laser powers. This problem has been solved by using the approach known as Brillouin optical time-domain analysis.

The fiber optic sensor has been already tested and showed the opportunity to measure the temperature of a hot spot to within 3 degrees Celsius from the end of a 10-kilometer long optical fiber. Additionally, it is planned to improve the distributed sensor and make it even faster resulting in the further reduction of the acquisition time. Future enlargement of sensing point density will promote the fiber sensors being used in new fields, for example, biomedical applications.

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 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

Fiber optic solutions for fire detection and temperature measurement

FBGs for fire detectionProper fire detection in the mining area is the number one priority because fire can evoke damages to valuable assets, downtime in operation, and even loss of lives. Herewith, the installation of fire protection devices can be complicated by harsh environmental conditions of the mining area because industrial equipment produces dirt, dust, humidity, and corrosive atmospheres in the production, storage, or transport of goods. Nevertheless, the application of modern fiber optic sensors based on distributed temperature sensing or DTS is considered to be a proven and efficient technology for fire detection and temperature measurement.

The fact is DTS technology provides precise temperature measurement along the length of a conveyor belt due to the use of autonomous fiber optic cables, therefore, even very long conveyor routes can be efficiently monitored. Thus, cases of fires and overheating during mining operations can be quickly and easily identified and localized to within one-meter precision by distributed temperature sensors, enabling to activate the safety countermeasures. Also, it should be mentioned that it is required the proper installation of the fiber optic sensor cables and adjustment of the alarm zones for heat detection of industrial rollers.

Nowadays mining industry applies fiber optic linear heat detection systems for these purposes, however, the new distributed sensing technology may significantly improve and increase the protection of assets in combination with the one mentioned above. The principle of DTS technology operation is based on the use of optical fibers as a distributed microphone, moreover, it means that fiber optic sensors allow measuring not only the temperature but also the acoustics. Such additional information is important because it helps to determine potential sources of danger and improves the whole purpose of fire prevention. To be precise, the DTS is highly important in hot roller detection that is the main reason for conveyor fires.

Also, it is difficult to identify the initial smoldering stage with traditional techniques, herewith, the majority of common gas detecting systems do not work properly because of high air currents. An optical fiber-based on distributed temperature sensing technology, in its turn, provides numerous benefits during both normal operation and dangerous situation that include:

  • Reliable fiber optic cable that is resistant to dirt and dust;
  • Long-distance (up to 10 km) and up to 4 measurement channels monitor several conveyors with one DTS system;
  • Practically maintenance-free;
  • Accurate localization of fires and hot rollers;
  • DTS is able to detect fires in spite of unfavorable environmental conditions.

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

Fiber Bragg grating sensors provide groundwater flow sensing

FBG sensors for flow sensingGroundwater flow sensing is highly important when it comes to the extraction of drinking water because it allows for avoiding well clogging and pollution. Nevertheless, fiber Bragg grating sensors with optical fibers are considered to be a promising new technique for monitoring of groundwater flow.

 

The fact is that FBG sensors enable us to identify even tiny changes in temperature, pressure, and fiber shape taking into account the sensitivities influenced by the packaging. Thus, fiber Bragg grating sensors are able to create a multiplexed sensor for the groundwater flow direction and magnitude.

It should be mentioned that the fiber-optic technology of FBG sensors has numerous application range, for example, in aerospace (load monitoring and shape sensing), in civil engineering (structural health monitoring), and in the oil and gas industry (temperature and pressure monitoring).

Today the technology of fiber Bragg grating sensing is also used for groundwater flow monitoring. FBG sensors allow measuring various physical properties, strain, or temperature variations such as pressure, vibrations, and curvature of the optical fiber, herewith, fiber sensors make instant and precise measurements.

One more technique that can be used for monitoring is distributed temperature sensing, and the intended application influences directly the choice of technology – fiber Bragg grating or DTS sensing. DTS uses conventional single-mode or multimode fibers that find various applications in the telecom industry, that is why DTS fibers are available in large lengths.

Moreover, the FBG sensors are possible to be written in traditional and specialty fiber optics, and consequently, their price increases per sensor number. However, the cost of fiber interrogators that are required for the DTS sensing data collection is five times more expensive than FBG units.

Traditional fiber Bragg grating sensors already possess a sufficient temperature resolution for the measurement of groundwater temperature changes without additional packaging. In addition, this FBG system has been recently tested to demonstrate its benefits for groundwater flow monitoring.

Thus, the experiment has shown that the use of FBG sensors enables to measure the relative temperature with a precision of 0.85 ℃ for the differential measurements. Also, the used fiber Bragg grating system is able to make a multiple-sensor interrogation with the possibility of an expansion into a larger distributed sensing network.

Finally, the data results presented that fiber Bragg grating sensors can be employed as a temperature sensing system in the subsurface environment, but in this case, they did not demonstrate any benefits over the existing fiber sensing technologies. Nevertheless, multiplexed fiber Bragg grating pressure or strain sensors would possibly find their application in groundwater flow monitoring.

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. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com