Calibration and characterization of a CW radar for blade tip clearance measurement

The calibration and characterization of a blade tip clearance sensor is proposed for gas turbine applications. This sensor is based on continuous-wave microwaves that operates at 6GHz in the version for large frame turbines. The calibration of such a sensor is a difficult problem because of the complex interaction between the microwaves and the blade tip geometry. Different geometrical parameters can influence the calibration results, which drives us towards using both the actual blade geometry and probe positioning. This study presents the calibration process of this sensor using a precision test setup. Moreover, the optimization of probe positioning is discussed in order to limit the measurement errors due to axial shift of the rotor during engine operation, which is the major source of errors for tip clearance measurement. Finally, the measurement error corresponding to an optimal probe positioning is characterized.