Ratiometric Sensor System for Turbine Clearance Measurement
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Solution Overview
Problem
Existing sensor systems for measuring clearance between objects, such as turbine blades and shrouds, face inaccuracies due to calibration drift and noise, especially in applications where the target object's geometry changes, leading to ineffective in-service measurements.
Innovation Solution
A ratiometric sensor system that generates multiple signals from sensors positioned at different locations to calculate clearance using a ratiometric technique, reducing noise and drift by processing signals from capacitive, microwave, or optical sensors, and employing a reference geometry for accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single capacitance probe is used to measure clearance, then the measurement system is simple, but measurement accuracy deteriorates due to calibration drift when target geometry changes
Solution Approach 1:
The patent divides the measurement system into multiple sensor elements (first sensor and second sensor) that generate separate signals. By segmenting the measurement function across multiple sensors, the system can process signals differently to eliminate drift effects, thereby maintaining measurement accuracy without excessive complexity
Solution Approach 2:
The patent changes the measurement parameter from a single capacitance value to a ratio of two capacitance values. This parameter transformation allows the measurement system to eliminate common-mode drift effects by taking the ratio of signals from two sensors, thereby maintaining accuracy despite geometry changes
2Ease of manufacture
If a single probe measures clearance on rotating components, then the system is simple to implement, but measurement reliability deteriorates due to noise from thermal distortions in connecting wires
Solution Approach 1:
The patent uses two separate sensor signals instead of a single probe signal. By segmenting the measurement into two independent signal paths, the system can process them differentially to reject noise and thermal distortion effects, improving reliability while maintaining reasonable implementation complexity
Solution Approach 2:
The patent employs a feedback mechanism where the ratio of two sensor signals is continuously monitored and processed. This feedback approach allows the system to compensate for thermal distortions and noise by comparing the relative changes in both signals, thereby maintaining measurement stability
3Measurement precision
If offline clearance measurements are taken during design and testing, then initial calibration is achieved, but measurement effectiveness deteriorates during in-service operation due to part wear
Solution Approach 1:
The patent transitions from static offline calibration to dynamic in-service measurement. By using the ratio of two continuously varying sensor signals during operation, the system adapts to changing conditions including part wear, thereby extending the measurement validity period from initial calibration only to throughout the service life
Solution Approach 2:
The patent changes from fixed calibration parameters to dynamically calculated ratio parameters. By continuously computing the ratio of two sensor signals during operation, the system maintains measurement precision despite changes in part geometry due to wear, effectively extending the measurement validity throughout the component's service life
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
The system provides accurate and stable clearance measurements, enabling effective in-service control of parts, even as they wear, by minimizing calibration drift and noise, and maintaining precision over time.
Implementation Method 1
In certain applications, a capacitance probe is employed to measure the distance between two objects. The probe is located on one of the objects and measures a capacitance with respect to the other object for estimating the clearance between the two objects.
Data Source
AI summary
A system for measuring clearance between a first object and a second object is provided. The system includes a sensor configuration to generate a first signal representative of a first sensed parameter and a second signal representative of a second sensed parameter. The system also includes a clearance measurement unit configured to process the first and second signals based upon a ratiometric technique to calculate clearance between the first and second objects.