Research on a large-range three-coil coaxial optical fiber displacement sensor

Abstract

A large-range three-coil coaxial optical fiber displacement sensor for measuring the air gap of a direct-drive wind turbine is designed in this paper so as to overcome the problem that the traditional reflective optical fiber sensor has a small measuring range. The mathematical model of the modulation function of the three-coil coaxial large-range fiber displacement sensor is established by using the simplified geometric optical reflection spot model, so that the ratio compensation mechanism under different combinations is analyzed and compared, and the parameters affecting the characteristics of the sensor, including the fiber core radius R and the numerical aperture NA of the transmitting fiber, and the number of receiving fiber loops in the second, third and fourth layers of the sensor probe are analyzed by simulation. The results show: As the number of laps of the receiving fiber turns, the sensor range is significantly improved, and its sensitivity is improved, but the corresponding initial dead zone is also increased; the smaller the numerical aperture of the transmitting fiber, the larger the linear range of the output characteristic curve; the larger the radius of the fiber core, the larger the linear range of the output characteristic curve, but the corresponding initial dead zone becomes larger and the sensitivity is reduced, so that the final selected design parameters of the system are given by analysis. Finally, through the sensor characteristics experiment, the actual measurement range of the sensor probe is consistent with the theoretical simulation results, and its measuring range can reach 3.5mm- 8.5mm.