Community Research and Development Information Service - CORDIS

Fibre bragg grating inclinometer

Optical Fibre Bragg grating-based uni-angular inclinometers have been designed, realised and tested by CEA-LETI. A hanging mass submitted to gravitation is allowed to rotate with respect to an upper part fixed to the inclinometer’s body itself moving with the structure. The angle is turned into a proportional strain applied to two pre-strained FBGs that behave differentially (one FBG is strained while the other is compressed). Angular rotation effect is thus doubled whereas temperature and pressure effects are cancelled out therefore providing environmental compensation.

Inclinometer prototypes have been tested with respect to required accuracy, detection limit and mechanical hysteresis. Angle resolution is about ± 10 arc seconds that corresponds to a 1meter high wall displacement of 50 mm. The range is +/- 2.5 degrees and the residual temperature sensitivity is lower than the angle resolution.

Several inclinometers, in compact and waterproof packaging have been tested along with traditional inclinometers on a field trial at Toulon, France and interrogated with the portable CEA FPI-based logging unit. This field trial have shown better performance in comparison with usual inclinometers opening the way to intelligent public work methods (compensation grouting) thanks to the accuracy and portability of the instrumentation.

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