Capacitive Clearance Measurement Using Reference Geometry
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Solution Overview
Problem
Existing clearance measurement systems for rotating machines are ineffective for in-service measurements due to noise and calibration drift, failing to accurately account for changes in temperature, oxidation, and wear, leading to inaccurate clearance control.
Innovation Solution
A clearance measurement system that uses a capacitive probe with a multilevel reference geometry to generate time-varying signals, processing the difference in capacitance measurements between the rotating component and the reference geometry to estimate clearance, thereby minimizing calibration drift and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitance probe is used to measure clearance between rotating and stationary components, then a direct current voltage based measurement is obtained, but the measurement does not account for changes in clearance due to temperature changes, electronic drifts, oxidation, and other factors
Solution Approach 1:
The continuous surface of the rotating component is segmented by introducing reference geometries (notches, grooves, or slots) at known positions. This segmentation creates discrete measurement points that can be individually tracked throughout rotation, allowing the system to distinguish between true clearance changes and artifacts caused by temperature drift, oxidation, or electronic instability.
Solution Approach 2:
The system uses the known positions of reference geometries to create a feedback mechanism where measured clearance values at these reference points are compared against expected values. This feedback loop allows the system to compensate for temperature changes, electronic drifts, and other interfering factors by continuously adjusting measurements based on the stable reference geometry positions.
2Measurement precision
If clearance measurement systems are used during design and offline testing, then clearance measurements can be obtained, but the measurements become ineffective for in-service clearance control due to noise and drift generated by changes in component geometry
Solution Approach 1:
The system transitions from static offline measurements to dynamic in-service measurements by utilizing the rotation of the component itself as a mechanism for measurement. The rotating component carries reference geometries that passively provide stable measurement points throughout rotation, enabling the system to adapt to in-service conditions while maintaining measurement accuracy.
Solution Approach 2:
The rotating component serves dual purposes: it is both the object being measured and the carrier of the reference geometries used for measurement. This self-service approach eliminates the need for separate calibration standards or external reference objects, allowing the system to maintain measurement accuracy during operation without requiring external intervention or recalibration.
3Measurement precision
If a capacitive probe measures clearance, then a static output in time is obtained, but the measurement cannot detect changes in clearance over time due to the nature of direct current voltage measurements
Solution Approach 1:
The system utilizes the periodic rotation of the component to convert static capacitance measurements into dynamic time-varying signals. As reference geometries pass the sensor location during rotation, they create periodic variations in the measured capacitance, enabling the system to track clearance changes over time while maintaining the simplicity of capacitive measurement technology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, self-calibrating clearance measurement during operation, reducing the impact of noise and drift, and allowing for real-time monitoring and control of clearances between rotating and stationary components.
Implementation Method 1
a sensor disposed on said stationary component, wherein the sensor is configured to generate first signal and second signals representative of first and second parameters corresponding to the continuous surface of the rotating component and the reference geometry, respectively
Data Source
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AI summary
A clearance measurement system (12) is provided. The clearance measurement system (12) includes a reference geometry (86) disposed on a first object (14) having an otherwise continuous surface geometry and a sensor (64) disposed on a second object (16), wherein the sensor (64) is configured to generate a first signal representative of a first sensed parameter from the first object (14) and a second signal representative of a second sensed parameter from the reference geometry (86). The clearance measurement system (12) also includes a processing unit (198) configured to process the first and second signals to estimate a clearance between the first and second objects (14, 16) based upon a measurement difference between the first and second sensed parameters.