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Bragg grating sensor for torsion and temperature measurements in rotating machinery

Torque sensing on rotating shafts is important for monitoring electrical and internal combustion machines, especially for real-time computer control. Optical fiber sensors are ideally suited to this application because of many desirable properties such as immunity to electromagnetic interference, their multiplexing capability and small size. This paper discusses a dual fiber Bragg grating sensor for the independent measurement of temperature and torsion in a rotating shaft. It shows theoretically that whereas torsion affects the differential wavelength of the gratings in the proposed configuration, temperature changes in principle only the common-mode wavelength. These characteristics of the system allow one to measure both torsion and temperature with the same sensing system. For the particular system investigated experimentally, the differential wavelength change was 19.4 pm/Nm, and the corresponding temperature sensitivity was -0.67 pm/°C. In contrast to these values, the temperature sensitivity of the common-mode wavelength was 25.4 pm/°C, and its torque cross-sensitivity was -0.19 pm/Nm.