An industrial need …

Reliable high temperature measurement is vital to ensure the success of a wide range of industrial processes”.

Highly technological sectors such as aerospace, nuclear fuel production, essential nuclear safety tests and electric cars manufacture, or heavy industries including the production of refractory metals (silicon carbide, carbon/carbon composite materials, …), iron, steel, glass and ceramics are some examples of industries that perform operations in extreme conditions. They require advanced technologies for high quality/reliability temperature measurement in harsh environments.

“The measurement of high temperatures in industry is subject to large uncertainties due to non-ideal measurement conditions”.

The use of contact electrical sensors such as type K and B thermocouples have the great advantage of being able to be used in places that have accessibility restrictions. However, they suffer intrinsic problems of long-term reliability due to progressive contamination and gradual aging. Such degradation occurs due to the severe environmental conditions of the industrial processes (high temperature, corrosion by a variety of chemicals…), causing detrimental and unpredictable drifts in the contact thermometry and implying intensive and costly maintenance operations. In addition, the measurement quality of such sensors can be affected by external magnetic interferences, which can limit their use in applications where strong external electromagnetic fields exist.

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Radiation thermometry allows the determination of temperature without physical contact, which limits the inherent problems that sensors suffer when exposed to extreme operating conditions. However, the installation of radiation sensors is usually more complicated when the accessibility is restricted. The obtention of reliable measurement results with this technology is much more delicate due to the need to know exactly the emissivity and transmission window of the studied material, which also limits the overall versatility of such sensors.

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FBG fiber sensors, a promising technology …

“The use of fiber optic-based sensors that use light instead of electricity, and standard optical fiber instead of copper cable allows to measure temperatures with high quality/reliability in environments that operate in very extreme conditions.”.
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The use of a new type of sensors based on optical fibers for the measurement of high temperatures in very hostile conditions is gaining a huge interest at industrial level. This application has been greatly favored by recent innovations in optoelectronics and in the different manufacturing technologies of both passive components and optical cables, and recent improvements in assembly and connectorization techniques. These sensors have proven, without any doubt, to possess high accuracy and reliability of measurements and are positioning themselves as a relevant technology due to the inherent properties of optical fibers.

However, the optical fiber by itself is fragile and the sensors currently available on the market are usually coated by a layer of thermoplastic/metallic composite materials to give them mechanical strength while retaining the inherent flexibility of the fiber. Such coatings are not suitable and greatly limit the practical applicability of this technology at an industrial level in processes that operate in very extreme conditions.

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“An application example: deformation sensors for civil engineering and industrial infrastructures monitoring”

FBG sensors technology is based on the alteration of the diffraction pattern which can be induced by changes of temperature of the surrounding atmosphere and/or by direct physical deformation (mechanical stress) of the optical fiber.

CalSens, a spin-off of the Polytechnic University of Valencia, develops FBG sensors which can be easily inserted into civil engineering and/or industrial infrastructures.

Such implementation of the optical sensors allows the in-situ monitoring of the deformation of said structures, either during initial load tests or for long term monitorization acting as safety devices and easing the predictive maintenance.

CalSens Website

Our proposal

To expand the measurement ability and industrial applicability of current fiber optic sensors, the InTenSO project aims to develop an innovative coating that provides complete compatibility to work in extreme conditions. Such coating will ensure improved chemical and mechanical resistance and adequate flexibility to facilitate the implementation of the temperature sensors in harsh operative conditions processes where the accessibility is restricted. The final product will be able to safely work in explosive atmosphere and will be fully compatible with high level radiofrequency environment.

About us

Owing the multidisciplinary aspect of the InTEnSO project, two complementary research groups of the Universitat Politècnica de València (UPV) are involved in the development of the proposed technology. Members of the Institute of Chemical Technology (ITQ) bring their knowledge about the synthesis of inorganic materials while members of the Photonics Research Labs (PRL) group, belonging to the Institute of Telecommunications and Multimedia Applications (iTEAM), bring their knowledge in the field of photonics and signal processing.

How FBG sensors work …

Sensor Fiber Bragg Grating (FBG)

A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. The wavelength (λ) of the reflected light depends on the spacing of a periodic variation or modulation of the refractive index of the fiber core, which gives rise to a series of dielectric mirrors for certain λ.

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Red de sensores por multiplexación …

The sensing function of an FBG originates from the sensitivity to externally applied thermal perturbations of both the refractive index of the optical fiber and the grating period within the fiber. The temperature sensitivity of the FBG is mainly due to the thermo-optic effect i.e., temperature-induced change in the glass refractive index and to a lesser extent, on the thermal expansion coefficient of the fiber.

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Key advantages of FBG technology …

• The optical fiber has a large bandwidth, which allows monitoring a many points / sensors in a single cable. In addition, very rapid variations of environmental signals can be measured.

• Its small weight and diameter makes it easy to embed in all kind of pieces without altering their properties. The diameter of the standard fiber is of only 100 microns and its low weight makes it ideal in more specialized applications such as the aeronautical and space industry.

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