Study on suppressing Doppler effect and non-linearity simultaneously in dynamic clearance measurement of Frequency Swept Interferometry

Frequency-swept interferometry (FSI) is a well-established technique for static ranging or clearance measurement. However, when measuring the dynamic clearance in turbines, both the FSI-Doppler effect induced by target drift and the sweeping nonlinearity of the light source restricts the measurement accuracy significantly. These are two inevitable problems and must be solved. Therefore, an improved FSI-based system is proposed to realize the dynamic clearance measurement. The system consists of two sensing arms and one reference arm. Two sensing arms refer to an FSI and a frequency-fixed interferometer (FFI) with an acoustic optical modulator (AOM), while the reference arm contains a determined Machzender interferometry. The Machzender interferometry is adopted to correct the nonlinear error of the FSI signal, and the FFI with the AOM is used to suppress the Doppler error. An optimized fusion algorithm will be used combining the information of three arms. And the dynamic clearance can be reconstructed at each sampling point with the algorithm suppressing the Doppler effect and the sweeping nonlinearity problems. The system with its algorithm was verified theoretically by measurement simulations for targets in multiple forms of motion. Further experiments will be carried out in the near future.