Distributed Temperature Sensing (DTS)

Distributed Temperature Sensing (DTS)
The last decade we saw an increase in the application of glass fibre technology to measure temperature, elongation, vibration and displacement over long distances. Distributed Temperature Sensing (DTS) is one example of this type of technology. The measurement principle is based on the optical Raman back-scattering of laser pulses that are sent into the glass fibre. The relationship of line intensities from the Stokes and the Anti-Stokes Raman scatter contains temperature information. Combining this with the time of flight information of the back-scattered pulses this will result in a temperature profile along the glass fibre. Typical claims for spatial and temperature resolutions are 1m and 0.1K respectively. In general, the accuracy is better than 1K and the range varies from 1 to several tens of kilometres. The stability and accuracy of these systems depend on an important degree on the internal or external reference used in the system. Another important factor is that the glass fibre can suffer from splice connections, bending losses and ageing, such as may occur in chemically aggressive or hot environments. The wide variety of technical implementations of DTS and other glass fibre measurement systems, as well as the different environmental conditions, emphasise the importance of thorough testing, validation and calibration.

Limits of system performance
VSL develops testing and calibration facilities to be able to provide reliable and independent information regarding the performance of DTS systems. VSL investigates the limits of system performance under a range of conditions. Fundamental research is performed into the noise characteristics - the signal fluctuations over time as well as distance – of different systems. This yields important insights that can be used to design DTS measurement systems for a range of applications. And finally, we investigate methods for accurately determining the distribution of glass fibres in a cable. This is because the glass fibre is always slightly curled and folded in the cable and this translates directly into uncertainty regarding the position of the measured temperature profiles.