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DTS - DISTRIBUTED TEMPERATURE SENSING SYSTEMS
A DTS - Distributed Temperature Sensing system based on fiber optics is a technology used for measuring temperature along the length of an optical fiber. The system utilizes the principle of Raman scattering to detect the temperature changes in the fiber.
In a fiber-optic-based DTS system, a laser source is used to transmit light through the fiber. As the light travels through the fiber, a small portion of the light is scattered back towards the source due to the Raman effect. The intensity of this scattered light is proportional to the temperature of the fiber at that point.
The scattered light is collected by a detector and processed by a computer to determine the temperature profile along the fiber. By using advanced signal processing algorithms, the system can provide high spatial resolution and accuracy.
A distributed fibre optic cable (FireFiber) is connected to the FireLaser Distributed Temperature Sensing System (DTS System), which measures temperature and distance data of thousands of points along the cable's length.
Installed inside the asset that has to be safeguarded, the fibre optic cable serves as the sensing component.
Based on the determined temperature profile, the FireLaser Sensor Control Unit generates alarms.
So, with unparalleled accuracy, the FireLaser Distributed Temperature Sensing System can locate a hot spot on a fibre optic cable that is up to 5 kilometres long.
The system can track the movement of a hot spot or numerous hot spots in real-time as well as in terms of their physical location and temperature.
With the use of FireLaser Distributed Temperature Sensing Technology,
DTS systems have a pulsed laser that enters the fibre optic with an approximately 1m pulse (10ns in duration). The pulse interacts with the glass as it moves along the fibre optic cable's length.
A very little portion of the initial laser pulse is reflected back towards the DTS sensing system due to minute flaws in the glass.
The Distributed Temperature Sensing System can determine the temperature of the event (by examining the intensity of the reflected light) and the event's location (by observing the amount of time it takes for the backscattered light to return) to within typically a metre of each other.
DTS technology typically employs a conventional telecoms fibre optic connection; only readings at temperatures above 100°C necessitate the use of specialised cables or sensing stations.
For shorter ranges (up to 40 km), the sensing fibre is commonly based on multimode fibres, and for longer ranges, on single mode fibre (40-100km). Distributed Temperature Sensing System technology typically employs a conventional telecoms fibre optic connection; only readings at temperatures above 100°C necessitate the use of specialised cables or sensing stations .
For shorter ranges (up to 40 km), the sensing fibre is commonly based on multimode fibres, and for longer ranges, on single mode fibre (40-100km).
Distributed temperature sensing systems can often measure the temperature with an accuracy of ±1°C and a sensing resolution as low as 0.01°C at a distance of 1m (this is known as spatial resolution).
The relationship between measurement resolution, range, and sampling time, on the other hand, is inverse; that is, the temperature resolution declines with range and increases the longer it takes to collect data for a given measurement.
Profile with Rayleigh and Stokes Bands Fiber optics are made from doped quartz glass and when laser light is transmitted in a fiber optic an interaction occurs between the light particles (photons) and the electrons of the molecule. At a particular frequency in the electromagnetic spectrum (known as the Stokes and anti-Stokes bands), light scattering, also known as Raman scattering, occurs in the fiber optic. The intensity of the so-called anti-Stokes band is temperature-dependent, while the so-called Stokes band is practically independent of temperature. The local temperature of the optical fibre is derived from the ratio of the anti-Stokes and Stokes light intensities.
For distributed sensing technologies, optical time domain reflectometry (OTDR) and optical frequency domain reflectometry are the two fundamental measuring techniques (OFDR).
The principle for OTDR is quite simple and is very similar to the time of flight measurement used for radar. Essentially a narrow laser pulse generated either by semiconductor or solid state lasers is sent into the fibre and the backscattered light is analysed. From the time it takes the backscattered light to return to the detection unit it is possible to locate the location of the temperature event.
