The reflection wavelength of the FBG (Bragg wavelength) depends on the grating characteristics (period, modulation) and is influenced by the ambient conditions such as strain and temperature. This allows the utilisations of FBGs as sensor for strain and temperature.
In the case of temperature sensing the Bragg wavelength is a function of the temperature. This temperature dependence results from changes of the refractive index of the fiber as well as from thermal expansion of the glass material.
The use of Draw Tower Gratings (DTGs) for temperature sensing enables several advantages compared to electrical sensors as well as to classical FBGs:
- Temperature measurements using FBGs is an absolute measurement.There is always a unique relationship between wavelength and temperature.
- FBGs have due to their small size and volume a fast temperature response time which is needed for the measurement of fast temperature changes.
- FBG based temperature sensors can become read out over large distances, without the need of amplification means under way (>20km).
Due to the nature of the glass, FBG based temperature sensors show a good corrosion resistance.
FBG based temperature sensors are immune to electromagnetic interference (even lightening interference)
- FBG based temperature sensors are intrinsically passive (no electrical power required) and therefore can be positioned in high voltage and potentially explosive atmosphere areas.
- Due to the low thermal conductivity of the lead-in fiber (glass), FBG based temperature sensors have no significant influence on the distortion of the thermal distribution profile to be measured.
- DTG based temperature sensors can be used in series configuration with multiple gratings in a spliceless fiber (e.g. 80 sensors in 80 cm fiber) allowing to perform distributed measurements were the available space is limited.
- Ormocer coated DTGs can be applied in high temperature environments up to 200°C as well as in cryogenic environments, down to the liquid He temperatures.
FBGS has developed a broad product portfolio of different temperature sensors based on Draw Tower Gratings. However, different other companies are also offering high reliable temperature sensors based on our DTGs. For more information, please contact us.