Distributed Fiber Optic Sensing
As it travels down a fiber optic strand, light is naturally backscattered. The backscatter pattern is affected by changes of temperature and other phenomena, see below. Analysing these backscatter patterns detects small changes in temperature (or other other phenomena).
As the propagation time of light at each wavelength is known precisely, the location of associated changes indicates the location of the event. These physical changes of the fiber along its length provide Distributed Sensing.
Types of Distributed Fiber Sensing
Fiber optic distributed temperature sensing, introduced in late 1990s, measures and monitors the temperature of a wide range of industrial assets. Its ability of its inert sensor to provide continuous, real-time temperature data over long distances (many miles from a single interrogator) makes it ideal for monitoring linear and inaccessible assets, like power cables and pipelines.
The fiber optic cable acts as the sensor all along its length. Measurements of temperature are possible to within 1 or a few degrees, spatial resolution down to approximately 1 foot.
Inert, robust, light and flexible, optical fiber is sensitive all along its length. It is immune to EMI, dirt, dust and humidity.
Fiber optic cable configurations to suit most projects
Introduced to the telecoms industry in 1980s, the fibers are usually incorporated into a multi-fiber cable, suitable for direct burial and use in harsh environments. A variety of cable structures and materials ensures that there is a cable suitable for cost effective monitoring of each project, whether it be sensing the temperature a power cable, a pipeline, or detecting fire in a road or rail tunnel. Radiation resistant cables are available for applications in nuclear power plants.
Multimode fiber – usually shorter distances
Single mode fiber – usually longer distances.
Scattering from light pulse as it travels through the optical fiber
During the passage of a light pulse through the fiber, backscattered light is produced.
Signal processing of the backscattered light provides information about the event
Analysis of the backscattered light identifies and gives the extent of the temperature events. Time-of-flight calculation identifies its location.
Standard cabinets are available, with UPS, battery and extra ventilation or protection options.
The temperature of the asset can be shown in graphical format. The temperature profile, history and zone data of the asset are available for diagnostics.
Alarms are shown visually, sent to SCADA/DCS or email/phone.