In-situ calibration of in-service strain sensing systems under passive excitation: methodology and impacts assessment

Aiming at the calibration of in-service strain sensing systems for structural health monitoring (SHM), a calibration method adapting to complex in-situ conditions is proposed. A calibration framework composed of measured variable, excitation source, reference system and sensing system is defined. By analysing the mechanism of in-situ calibration, two measurement models are deduced for instantaneous and intermediate errors of the sensing system respectively. To discover the effects of the ambient temperature on the calibration process, the experiments are conducted using a temperature test chamber, and then the qualitative analysis and quantitative estimation are performed. The results show that: (1) With the variation of temperature, the responses of both resistance strain gauges (RSS) and fiber optic strain sensors (FOS) change visibly; (2) The relative strain deviations between the sensing system (SS) and the reference sensing system (RS) within -10℃~50℃ fluctuate in a narrow range, for example 0.015~0.023 for RSS and 0.382~0.404 for FOS in this study; (3) The range of the deviations between SS and RS that is affected by temperature can be estimated with the proposed method, for example, 4.6μe for RSS and 18.1μe for FOS, respectively, with a confidence level of 95%.