Distributed temperature sensing uses fiber optic cables to detect temperature differences in remote or underground locations. Laser light scatters when there are variations in strain or temperature, allowing for accurate temperature monitoring over long distances. Fiber optics are durable and resistant to electrical interference, and can be used in temperatures above 700°F. The technology is cost-effective and can be combined with strain measurement for leak monitoring. It has seen growing interest for environmental monitoring of land and water resources.
Distributed temperature sensing is the use of fiber optic cables to detect temperature differences in electrical installations, tunnels, underground wells and lakes or streams. Fiber optic cables use a laser to transmit a specific wavelength of light along the length of the cable. Variations in strain or temperature cause laser light to scatter, and sensing systems and software allow the location and magnitude of the temperature difference to be determined with excellent accuracy.
Using distributed fiber optic temperature sensing, temperatures can be monitored over long distances, making it an ideal technology for temperature monitoring in remote or underground applications. The light scattering characteristics of optical fibers can also measure cable strain and temperatures. Distributed temperature sensing can be combined with strain measurement for leak monitoring of pipelines or dams.
Fiber optic cables use silicon dioxide glass fibers with a particular molecular arrangement that allows laser light to travel long distances with little force reduction. Local temperatures outside the fiber cable change the molecular structure of the glass fiber and can be measured by corresponding changes in the backscattered light measured at both ends of the optical cable. Light detectors and software programs are used to measure and quantify the amount of light that is lost and thus the local temperature change. The properties of the fiber optic cable also allow the location of the temperature change to be calculated with good accuracy.
Distributed temperature sensing systems have been implemented that can monitor temperatures over distances greater than 18 miles (30 km). Fiber optics also tend to be durable, resistant to electrical interference, and can be used in temperatures above 700° Fahrenheit (about 370° Celsius). Unlike thermocouples or infrared temperature systems, distributed temperature sensing is continuous along the entire length of the optical fiber. The software can show temperatures anywhere in the fiber optic cable continuously, not just at specific points.
The only material that needs to be installed over long distances is optical cable, so with monitoring sensors and software analysis installed with laser transmission equipment, installation and maintenance costs are low. The light diffusion effects in fiber optics do not require any exotic materials or special cables, so fiber optic cables used for telecommunications can, in theory, also be used to monitor temperatures. This combination of uses for fiber optics has seen growing interest in the early 21st century for environmental monitoring of land and water resources, particularly as fiber optic networks have rapidly become widespread for high-speed telecommunications and internet connectivity.
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