Sensor for measuring blade tip clearance in gas turbines

A method for determining a distance between an inner surface of a stationary portion of a turbo machine that defines a gas flow path and a moving portion of the turbo machine within the gas flow path, comprising:

• generating, by a fixed gap capacitive probe, a first output signal which varies based on a characteristic of a gas in the gas flow path, wherein the fixed gap capacitive probe is located within a cavity defined in the stationary portion of the turbo machine and configured to sense a characteristic of a gas flowing through the gas flow path, the fixed gap capacitive probe having a pair of radially spaced conductive plates wherein a radially innermost conductive plate is located within the cavity radially outward from the inner surface of the stationary portion;
• generating, by a variable gap capacitive probe located within the cavity adjacent to the fixed gap capacitive probe, a second output signal which varies based on a distance between the variable gap capacitive probe and a moving blade of the turbomachine, wherein the variable gap probe is configured to capacitively couple to the moving blade of the turbo machine;
• and
• adjusting a value of the second output signal based on the first output signal to produce an adjusted output signal.

A proximity sensor for determining a distance between an inner surface of a stationary portion of a turbo machine that defines a gas flow path and a moving portion of the turbo machine within the gas flow path, comprising:

• a fixed gap capacitive probe located in the stationary portion of the turbo machine and configured to sense a characteristic of a gas flowing through the gas flow path and to generate a first output signal which varies based on the characteristic of the gas, the fixed gap capacitive probe having a pair of radially spaced conductive plates wherein a radially innermost conductive plate is located within the cavity radially outward from the inner surface of the stationary portion;
• a variable gap capacitive probe located adjacent the fixed gap capacitive probe, wherein the variable gap probe is configured to capacitively couple to the moving portion of the turbo machine and to generate a second output signal which varies based on a distance between the variable gap capacitive probe and the moving portion;
• and
• a signal processor configured to adjust a value of the second output signal based on the first output signal to produce an adjusted output signal;
• wherein the fixed gap capacitive probe and the variable gap capacitive probe are located within a cavity in the stationary portion of the turbo machine;
• wherein the cavity in the stationary portion of the turbo machine comprises a first end opposite a second end, the second end extending radially outward from the inner surface of the stationary portion and defining a flared portion toward the first end, and the second end adjacent to the inner surface having an inside diameter greater than an inside diameter of the first end.