Rotating machine component clearance sensing systems and methods

1. A system for measuring a clearance between a rotating machine component and an abradable layer on or in a casing of the rotating machine, the system comprising:

a sensor oriented to detect the rotating machine component as the rotating machine component rotates past the sensor; and

a sensor processor in electrical communication with the sensor and configured for:

determining, by rub detection obtained during a calibration, occurrence of a rub event for the abradable layer of the casing;

determining a distance between the rotating machine component and the sensor; and

determining the clearance based on the rub detection and the distance between the rotating machine component and the sensor.

2. The system of claim 1 , wherein the sensor processor is configured to detect the rub event using an accelerometer sensor embedded in the sensor or proximate to the clearance.

3. The system of claim 1 , wherein the sensor comprises at least a first sensing element and a second sensing element spaced apart from the first sensing element.

4. The system of claim 3 , wherein:

the sensor processor unit is configured for:

receiving a first waveform from the first sensing element; and

receiving a second waveform from the second sensing element; and

the distance between the rotating machine component and the sensor is determined by comparing the first waveform and the second waveform.

5. The system of claim 4 , wherein comparing the first waveform and the second waveform comprises determining a timing difference between the first waveform and the second waveform.

6. The system of claim 5 , wherein comparing the first waveform and the second waveform comprises determining a peak delta time between the first waveform and the second waveform.

7. The system of claim 5 , wherein comparing the first waveform and the second waveform comprises determining a first zero-cross timing for the first waveform and a second zero-cross timing for the second waveform.

8. The system of claim 7 , wherein comparing the first waveform and the second waveform comprises determining:

a difference between the first zero-cross timing and the second zero-cross timing; and

a slope of the first and second waveforms proximate to the first and second cross timings, respectively.

9. The system of claim 3 , wherein:

the first sensing element comprises a first permanent magnet, a first pole piece, and a first sensing coil; and

the second sensing element comprises a second permanent magnet, a second pole piece, and a second sensing coil.

10. The system of claim 3 , wherein:

the sensor comprises a magnet and a split pole piece;

the split pole piece comprises a leading pole and a trailing pole;

the first sensing element comprises the leading pole and a leading sensing coil around the leading pole; and

the second sensing element comprises the trailing pole and a trailing sensing coil around the trailing pole.

11. The system of claim 10 , wherein the pole piece or magnet is shaped like the rotating machine component.

12. The system of claim 3 , wherein the sensor comprises:

a split magnet or ‘U’ shaped magnet; and

a pole piece in a center of the split magnet.

13. The system of claim 3 , wherein the sensor processor is configured for performing the calibration based on one or more of: engine speed, sensor temperature, and/or blade temperature.

14. A method for measuring a clearance between a rotating machine component and an abradable layer on or in a casing of the rotating machine, the method comprising:

rotating the rotating machine component past a sensor;

detecting, using the sensor, the rotating machine as the rotating machine component rotates past the sensor;

providing a sensor processor that is in electrical communication with the sensor;

determining, during a calibration, using the sensor processor and by rub detection, occurrence of a rub event for the abradable layer of the casing;

determining, using the sensor processor, a distance between the rotating machine component and the sensor;

determining, using the sensor processor, the clearance based on the rub detection and the distance between the rotating machine component and the sensor.

15. A system for measuring a clearance between a rotating machine component and an abradable layer on or in a casing of the rotating machine, the system comprising:

a passive eddy current sensor oriented to detect the rotating machine component as the rotating machine component rotates past the passive eddy current sensor, wherein the passive eddy current sensor comprises at least a first sensing element and a second sensing element spaced apart from the first sensing element; and

a sensor processor in electrical communication with the passive eddy current sensor and configured for:

determining, by rub detection obtained during a calibration, occurrence of a rub event for the abradable layer of the casing;

receiving a first waveform from the first sensing element;

receiving a second waveform from the second sensing element;

determining a distance between the rotating machine component and the passive eddy current sensor by comparing the first waveform and the second waveform to determine a timing difference between the first waveform and the second waveform; and

determining the clearance based on the rub detection and the distance between the rotating machine component and the passive eddy current sensor.