An optical interrogation system for fiber Bragg grating (FBG) strain sensors suitable for use in wind turbine blade (WTB) composite I-beam structures has been developed and tested. An off-the-shelf MEMS-based tunable Fabry-Perot etalon is controlled with a real-time embedded digital signal processor to manage calibration, scanning, signal processing and communications with a host system. A single superluminescent diode sources broadband light to illuminate a single or arrayed set of FBG sensors. Reflected light from the sensors are routed to a photodiode, and is correlated with calibration data to determine strain delta. This interrogation technique has shown fast scanning rates (>10Hz) for each sensor and can accommodate over 15 sensors on a signal fiber cable. The system has been implemented as a rackmount test instrument and validated against both a fiberglass I-beam under cyclic loading and a fiberglass composite specimen under tensile loading. Testing demonstrated 1 microstrain resolution, a noise level of +/- 1 microstrain, and a strain measurement range limited only by the fiber optic cable mechanical properties. Final work will include ruggedizing the packaging, increasing sampling rate (>50Hz) and adressing minor firmware bugs.
Project end date: 01/23/07