New microwave sensor for on-line Blade Tip Timing in gas and steam turbines

Real-time Blade Tip Timing (BTT) in rotating machinery enables condition-based maintenance and blade failure prevention. In this paper, we propose a new 6 GHz microwave sensing system suitable for BTT in gas and steam turbines. The system working principle is similar to the short range radar technique, using probes mounted in the turbine wall, in direct view of the passing blades. The front end of the system consists of a miniature open-ended coaxial resonator sealed by a ceramic cap. Its principle of operation is simple and robust, thus well-suited for the turbine harsh environment, while the radiated TEM mode allows for insensitivity to mounting orientation. The probe was validated through simulation and prototypes were successfully tested. Measurements on prototypes showed improved spatial resolution on the waveform compared to an existing 6 GHz patch antenna probe, and superior resolution and measurement range compared to Eddy current probes used for BTT.