The temperature compensation effect of FBG sensors is crucial to their measuring accuracy. In the design of a FBG sensor, two FBGs are often adopted to subject positive and negative strains through two packaging methods including all grating pasting and two-end pasting after grating pretension. Temperature compensation of the FBG sensor is often realized by using the difference of the wavelength shift of the two FBGs as the sensing signal. In current reports, temperature compensation is performed based on the assumption that the wavelength shifts of the two FBGs are the same. However, the difference of the wavelength shift is also influenced by the packaging methods and the temperature changing environment. This work presents an experimental study on the temperature compensation effect of two pair different packaged FBGs under abrupt temperature changing environment. For each packaging method, two FBGs with same parameters are pasted on the upper and lower surfaces of an equal-strength cantilever and assembled in a shell to serve as a FBG sensor. Boiling water and ice-water mixture are used to pour on the shell to form abrupt temperature changing, whereas an adjustable thermostat provides slowly temperature changing environment. Experimental results shows that the temperature compensation effects for the two different packaging method are same(within 21pm) when slowly temperature changing slowly, however, the compensation effects are significantly degraded during abrupt temperature increasing (58 pm and 48 pm for all grating pasting and two-end pasting, respectively). The results can provide a scientific reference for the design of FBG sensors.
In engineering practice, especially in the structural health monitoring (SHM) of civil engineering, the deformation of concrete is usually small, so a strain sensor don’t need a large measuring range but a high sensitivity. This work presents the structural design, measuring and sensitization principle, and full test of an embedded FBG strain sensor for SHM of reinforced concrete. Two capillary steel tubes protected by a stainless steel tube and embedded with each end fiber of a FBG have been proposed, which possesses the capacity of strain sensitization and adjustment. Experimental results show that sensor provides a sensitivity of 4.2 pm/με in measurement range of ±300με, which is 3.5 times than the bare FBG with center wavelength of 1550 nm. Test results also demonstrate that the sensor possesses good repeatability and creep resistance, which is promising for applications in civil engineering.
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