Capacitive blade tip clearance measurements for a micro gas turbine

The efficiency of a gas turbine has an inverse relationship with the clearance between the rotor blades and the casing. Recent efforts in miniaturization of micro gas turbine engines have created new challenge in tip clearance measurement. This paper describes the development of a tip clearance measurement system, based on capacitive measurement for a palm-top micro gas turbine engine. The sensor uses a ratio-metric measurement principle with synchronous detector to measure the average tip clearance between the rotor blades and the casing. A surface modification of the nonconductive compressor is used to create an electrode opposing the casing. A measurement range of 100 μm was achieved with a resolution of 0.8 μm.