Technology Principles
Our technology monitors fiber optic cable to accurately determine the position and intensity of any temperature event along the fiber optic cable.
The technology monitors the entire surface of an asset to detect changes of less than 1ºC in real time.
Distributed temperature sensing (DTS) solutions utilize fiber optic technology to provide spatially distributed measurements over many thousands of individual points.
Based on analysis of Raman back-scatter signals in an optical fiber, DTS systems uses a combination of variations in backscattered light intensity and time domain reflectometry to create temperature against distance profiles.
The fiber acts as both sensing element and transmission medium. Many thousands of discrete measurement points can be achieved over distances up to 30km using a single fiber.
In Optical time domain reflectometry, it is the Rayleigh backscatter signature which is examined. The signal is unshifted from the launch wavelength. This signature gives information on loss, breaks, inhomogeneities along the length of the fiber.
A pulse of laser light is launched into the sensing fiber through a directional coupler (Figure 1).
Figure 1 - Optical time domain reflectometry
Light is scattered as the pulse passes down the fiber through several mechanisms including density and composition fluctuations (Rayleigh scattering) as well as Raman and Brillouin scattering due to molecular and bulk vibrations respectively.
A proportion of this scattered light is retained within the fiber core and is guided back towards the source. The signal returned to the source is split off by the directional coupler to a receiver.
In a uniform fiber, the intensity of this returned light shows an exponential decay with time. Knowing the speed of light in fiber, we can calculate the distance that the light has travelled down the fiber and variations in composition, temperature etc along the length of the fiber show up in deviations from a 'perfect' exponential decay of intensity with distance thus enabling the distance along the fiber of any event.
Raman signal comprises two elements - the Stokes and anti-Stokes lines which are shifted in wave length from the Rayleigh signal and can therefore be filtered from the dominant constituent of the total backscattered light. The longer wavelength Stokes line is weakly temperature sensitive but the intensity of the backscattered light at the shorter anti-Stokes wavelength increases in proportion to the temperature rise and vice vera.
By examining the information from the Raman signal and providing a data output, which graphically integrates this information, Sensa’s DTS technology, is able to monitor fiber optic cable to accurately and speedily notify the position and intensity of any temperature event along the fiber optic cable.
