Distributed Temperature Sensing (DTS)

Distributed Temperature Sensing Systems (DTS) are optoelectronic devices which measure temperatures by means of optical fibres functioning as linear sensors. Temperatures are recorded along the optical sensor cable, thus not at points, but as a continuous profile. A high accuracy of temperature determination is achieved over great distances.

The distributed temperature measuring system consists of a controller (frequency generator, laser source, optical module, HF mixer, receiver and micro-processor unit) and a quartz glass fibre (fibre optic) as line-shaped temperature sensor.

The design is three-channel, since an additional reference channel is required besides the two measurement channels (Anti-Stokes and Stokes). Corresponding to the OFDR system, the power output of the laser runs through the sinus-shaped frequency starting from a starting frequency in the kilohertz range through the ending frequency in the high megahertz range within a measurement time interval with the help of the High Frequency (HF) modulator. The resulting frequency shift is a direct measurement of the local resolution of the reflectometer. The frequency-modulated laser light is connected to the fibre optic-sensor via the optical module.

The continuously back-scattered Raman light is spectrally filtered in the optical module and converted into electrical signals by means of photo detectors. Then the measurement signals are amplified and mixed in the Low Frequency spectral range (LF range). The Fourier transformation of the averaged LF signals results in the two Raman backscatter curves. The amplitudes of these backscatter curves are proportional to the intensity of the Raman scattering of the viewed location. The fibre temperature along the sensor cable results from the amplitude ratio of the two measurement channels.