LIOS Technology produces distributed temperature sensing (DTS) systems which measure temperatures by means of optical fibres functioning as linear sensors. Temperatures are recorded along the sensor cable, thus not at points, but as a continuous profile. A high accuracy of temperature determination is achieved over great distances or large surfaces, whilst measuring times are short.


Controllers of the OTS product series are distributed temperature sensing (DTS) devices measuring temperature profiles along optical fibres. A single OTS device provides well-resolved spatial and temporal temperature profiles for up to 8 optical fibres with lengths of up to 16 km at a single ended multimode fibre, resp. upt to 30 km at a single ended singlemode fibre. Sensor fibres are immune to electrical interference and can be used in harsh environments. OTS controllers can be operated at remote locations without PC. They transfer data via standard network protocols to PC in control centres, SCADA or PLC systems.

Physical Background

LIOS OTS controllers use the effect of Raman scattering within optical fibres for temperature measurement. Laser radiation introduced in such a fibre is inelastically scattered transferring energy from or to vibrations of the glass molecular structure. Excitation of glass vibrations reduces the energy of the light photons and thus causes a signal at longer wavelength (Stokes signal). Annihilation of vibrations causes signals at shorter wavelength (anti-Stokes signal). The ratio of excitation and annihilation of vibrations depends on the portion of excited vibrations in the material and thus on the temperature. This effect allows for optical measurements of temperatures in fibres just by introducing laser light and by measuring the intensity ratio at the Stokes and anti-Stokes wavelengths. Spatial resolution is achieved by the optical frequency-domain reflectometry (OFDR) measuring technology.

Raman Effect - the principle behind OFDR Distributed Temperature Sensing

Raman Effect - the principle behind OFDR Distributed Temperature Sensing

Unique OFDR-DTS Measuring Technology

OFDR is a modulation technology to analyze the distance of signal sources. The light source is modulated at different frequencies and the amplitude and phase of signals coming back from the fibre are measured. The mathematical Fourier transformation of the amplitude and phase data provides the spatial distribution of the signal sources. This is an elegant method to gain high spatial resolution with a quasi-continuous light source. Distributed temperature sensing using OFDR is a proprietary technology of LIOS Technology that has been developed and optimized during the last 10 years. Essential benefits of the DTS based on OFDR are elimination of laser wear out by quasi-continuous operation of a semiconductor laser, clearly reduced requirements for costly fast detection electronics and signal-to-noise improvements achieved by the quasi-continuous excitation light and the narrowband detection scheme. In contrast to pulse techniques, OFDR does not suffer from pulse broadening, and it thus gives constantly high spatial resolutions over very long distances.

Sensing (DTS) based on Optical Frequency Domain Reflectometry (OFDR)

Sensing (DTS) based on Optical Frequency Domain Reflectometry (OFDR)

High Reliability and Industrial Strength

The semiconductor laser diode has been thoroughly type tested according the Telcordia GR-468 standard. It fulfils telecom standards with a medium lifetime of > 25 years. The entire system was comprehensively evaluated by various independent international bodies (e.g. the VdS, the association of German asset insurers) including EMC tests as well as endurance tests at accelerated aging environments. Field data of the huge installed base prove the exceptional high reliability of the controllers.

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Corporate head office:

LIOS Technology GmbH - Linear Optical Sensors
Schanzenstrasse 39
Building D9-D13
51063 Cologne (Köln)
Federal Republic of Germany

Tel: +49 221 99887-0
Fax: +49 221 99887-150

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Sales and technical support for North American market:

LIOS Technology Inc.
1400 Campus Drive West,
Morganville, New Jersey 07751
United States of America

Tel: +1 (732) 970 8062
Fax: +1 (732) 972 4410

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