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Types of Distributed Fiber Optic Sensors: Advantages of DTS and DAS

What are the types of distributed fiber optic sensors

In the field of fiber optic temperature and strain measurement, fiber optic Brillouin optical time-domain analyzer (BOTDA), fiber optic Brillouin optical time-domain reflectometer (BOTDR), and Raman fiber optic sensor (DTS) are three main distributed fiber optic sensors, each with its own advantages, disadvantages, and technical solutions for implementation.

Distributed fiber optic sensing technology, as a new type of sensor, has inherent advantages such as large capacity, long distance, high accuracy, and anti-interference, and has developed rapidly in recent years. Among them, the distributed fiber optic temperature sensing system (DTS) is the most successful representative of commercialization. It is based on temperature sensitive effects (temperature differences) to achieve distributed monitoring of linear assets (such as cables, tunnels, pipelines), and plays a role in application scenarios such as fire monitoring, high-temperature liquid leakage, and high-pressure gas leakage.

Distributed fiber optic temperature sensor is an advanced temperature sensor that utilizes Raman scattering effect and OTDR technology to achieve distributed measurement of the temperature field of sensitive optical fibers. It has the advantages of high sensitivity, anti electromagnetic interference, intrinsic safety, light weight, long service life, and high reliability. It can be widely used for temperature monitoring and fire alarm of power cables, subway tunnels, coal mine tunnels, oil storage tanks, and large building structures.

With the development of distributed fiber optic temperature monitoring (DTS) and distributed fiber optic sound monitoring (DAS) technologies, it provides an important means for distributed real-time monitoring in various environments. The main principle of DTS technology is to use the reflection principle of optical fibers and the temperature sensitivity of reverse Roman scattering of optical fibers, relying on the quantitative relationship between the propagation of light in the optical fiber and the temperature changes around the optical fiber medium to determine the temperature at the location of the optical fiber medium. The main principle of DAS technology is to use the principle of coherent optical time-domain reflection measurement to inject coherent short pulse laser into the optical fiber. When external vibration acts on the optical fiber, the internal structure of the fiber core will be slightly changed due to the elastic optical effect, resulting in changes in the back Rayleigh scattering signal and changes in the received reflected light intensity. By detecting the intensity changes of the Rayleigh scattering light signal before and after the downhole event, the current downhole fluid flow event can be detected and accurately located, thus achieving real-time monitoring of downhole production dynamics. Due to its characteristics of anti electromagnetic interference, corrosion resistance, and good real-time performance, optical fibers have greater advantages in dynamic real-time monitoring of underground production.

When the wall of the heating pipeline becomes thinner, the joints break, or the insulation layer is damaged, it can cause temperature anomalies in local pipe sections. Temperature sensing optical fibers and DTS sensors can timely capture these anomalies and display them on the temperature distribution curve. By setting up a remote monitoring terminal that can analyze and extract the location and temperature deviation of abnormal points, the alarm function can be achieved. When incidents such as manual/mechanical excavation, vertical and horizontal mechanical drilling, large vehicles or mechanical equipment passing over the pipeline, and other mechanical excavation events that may cause damage occur near the pipeline, the surface is subjected to an instantaneous excitation, generating seismic waves that propagate to the distance. The vibration signals propagate to the vibration monitoring fiber optic near the pipeline, and are monitored in real-time through DAS sensors. By analyzing the signals, alarms are selected and the location of the event source is accurately located.

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