A Self-temperature Compensation Method of Fiber Optic Gage Using for Strain Balances

The rapid development of fiber optic sensing technology has enriched the types of wind tunnel strain balances. Numerous wind tunnel tests and research institutions have carried out various work on the fiber optic balance (FOB) based on the fiber optic strain gage (FOSG). In hypersonic wind tunnel tests, the total temperature of airflow is so high that both the model and the balance will be heated by the heating airflow, resulting the thermal output of the FOSG which affects the accuracy of the FOB. In order to reduce the thermal output effect, a new self-temperature compensation (STC) method has been proposed in this paper, by subtracting thermal expansions between the balance and a STC structure. In addition, the structure can not only reduce the thermal output, but also achieve a strain amplification of the FOSG. The formulas of both strain amplification and thermal compensation of the FOSG with the STC structure were deduced, as well as finite element simulation and tests were carried out, which verified the effectiveness of the compensation structure. The results of theoretical derivation, simulation and tests showed that the strain amplification decreases with the increase of the distance of installation points of the FOSG, and there is a zero point in the thermal output. However, due to the simplification of the STC structure, there are deviations in the theoretical derivation which can only be used in the preliminary design. The agreements between experiments and simulations, verified the temperature compensation effectiveness of the STC structure.