Turbine blade-mounted sensor fixture for tip gap measurement

A method for measuring gas turbine blade tip and turbine casing radial clearance gap, comprising:

• providing a gas turbine with a rotatable rotor having a turbine blade with a radially outwardly projecting tip in opposed spaced relationship with a circumscribing turbine casing, defining a gap there between;
• providing a non-contact displacement sensor that is capable of generating a displacement data set indicative of actual displacement;
• providing a sensor fixture including a sensor retention mechanism for calibrating the displacement sensor position and a clamp mechanism for clamping the fixture to the turbine blade;
• coupling the displacement sensor to the sensor fixture and coupling the sensor fixture to the turbine blade with the clamp mechanism, so that the non-contact displacement sensor is capable of generating a data set that is indicative of actual displacement relative to the circumscribing turbine casing without relative movement there between;
• calibrating the displacement sensor position relative to the blade tip by moving the entire displacement sensor within the sensor retention mechanism without moving the previously tightened clamping mechanism;
• coupling a rotor rotational position sensor to the turbine capable of determining actual rotational position without rotor rotational movement;
• rotating the rotor so that the turbine blade tip sweeps at least a portion of the circumscribing turbine casing while generating the displacement data set with the non-contact displacement sensor and a rotational position data set that is indicative of actual rotor rotational position with the rotational position sensor;
• acquiring the displacement and rotational position data sets from any rotor rotational starting position with a data acquisition system that is coupled to the displacement and rotational position sensors;
• and
• correlating blade tip and circumscribing turbine casing radial clearance gap relative to rotational position with the displacement and rotational data sets in a data analyzer system that is coupled to the data acquisition system.