Investigation of the stability of FBG sensor measurements under various climatic conditions

The sensing elements used to measure various parameters, including strain, are not only expected to ensure the reliability of the measured values, but also the stability of the measurements over a long period of time when exposed to various environmental conditions. The paper presents the results of studying the stability of the readings of point fiber-optic sensors based on a fiber Bragg grating under various climatic conditions. During the study, strain of the optical fiber was measured at various levels of temperature and relative humidity, under an external load using a fiber Bragg grating inscribed in the core of the optical fiber. For the experiments, a special setup was created that allows fixing an optical fiber with fiber Bragg grating and applying an external load in the form of a suspended load. The duration of the experiments ranged from 550 to 900 hours. Humidity and temperature ranges correspond to the most common values at which fiber-optics sensors are operated. The data analysis showed that for the fiber-optic sensors the readings do not change significantly during the time at different relative humidity and air temperature, as well as at loads corresponding to 50 and 70 % of the maximum load for an optical fiber with a fiber Bragg grating inscribed by the phase mask method. This result indicates the possibility of the effective use of fiber-optic sensors based on a fiber Bragg grating for long-term measurements of strain in the ambient temperature range from - 40 to + 80 °C and relative humidity from 5 to 95 %.