Planar Spiral Inductive Sensor for Blade Tip Clearance
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Solution Overview
Problem
Current blade tip clearance measurement techniques face inaccuracies due to environmental factors, debris contamination, and limitations in sensitivity and practicality for small-scale rotary devices, particularly in detecting dynamic tip clearance variations along the camber line of rotating blades.
Innovation Solution
A high-sensitivity inductive sensor using miniature spiral planar coils with resonance frequency division multiplexing, capable of measuring blade tip clearance at multiple positions with improved sensitivity and resolution, mounted on the inner surface of a turbine engine casing, which generates a combined AC signal to measure inductance changes caused by the rotating blade position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical methods are used to measure tip clearance with high accuracy, then measurement precision is improved, but the system becomes sensitive to debris contamination and requires large through holes larger than 10 mm in diameter
Solution Approach 1:
The patent replaces optical measurement methods with inductive sensing technology. The inductive sensor uses electromagnetic fields to detect blade tip clearance, eliminating the need for optical paths that are susceptible to debris contamination. The sensor comprises a coil that generates an electromagnetic field and detects changes in impedance caused by the proximity of the conductive blade tip, providing contactless measurement that is immune to particulate interference.
Solution Approach 2:
The patent changes the measurement parameter from optical properties (light reflection, transmission) to electromagnetic properties (impedance, inductance). By measuring the change in electrical impedance of the coil as the blade tip approaches, the system achieves high measurement precision while avoiding the contamination issues inherent in optical systems. The impedance change is directly correlated to the blade tip clearance distance.
2Object-affected harmful factors
If microwave detection method is used, then debris contamination sensitivity is reduced, but measurement capability deteriorates when blade thickness is small
Solution Approach 1:
The patent uses high-frequency electromagnetic signals (inductive sensing) rather than microwave frequencies. The inductive coil operates at frequencies that create a concentrated electromagnetic field near the coil surface, enabling detection of small changes in blade thickness. The impedance change detected by the coil is proportional to the blade thickness, providing accurate measurements even for thin blades where microwave methods fail.
3Ease of operation
If non-intrusive inductive sensor with 3-D solenoids is used, then through hole requirement is eliminated, but sensitivity to relative vibration increases and ferrous material compatibility is reduced
Solution Approach 1:
The patent transitions from three-dimensional solenoid coils to two-dimensional planar spiral coils. The planar configuration reduces the sensor's height and creates a more compact structure that is less sensitive to vibrations perpendicular to the coil plane. The spiral geometry concentrates the magnetic field in a specific region, improving measurement reliability while maintaining the non-intrusive installation advantage of not requiring through holes in the casing.
4Ease of manufacture
If intrusive inductive sensors are used, then manufacturing cost and installation ease are improved, but measurement resolution deteriorates with minimum detection capability of only 50 um
Solution Approach 1:
The patent uses planar spiral coils fabricated on a flat substrate rather than traditional wound solenoid coils. This planar geometry allows for precise control of coil dimensions and spacing, enabling higher resolution measurements. The two-dimensional spiral pattern creates a concentrated magnetic field with better spatial resolution, reducing the minimum detectable clearance from 50 micrometers to significantly smaller values while maintaining ease of fabrication using standard PCB or thin-film deposition techniques.
5Adaptability or versatility
If multiple inductive sensors are used to measure tip clearance at multiple locations, then measurement coverage is improved, but device complexity increases
Solution Approach 1:
The patent makes a single inductive sensor multi-functional by enabling it to measure tip clearance at multiple locations along the blade camber line. The planar spiral coil geometry creates a magnetic field that extends over a broader area, allowing one sensor to detect clearances at multiple positions simultaneously or sequentially. This eliminates the need for multiple separate sensors and their associated circuitries, reducing system complexity while maintaining comprehensive measurement coverage.
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 sensor achieves accurate and simultaneous measurement of blade tip clearances with high resolution, capable of detecting variations as small as 10 um, suitable for high-speed rotating machinery, and reduces complexity in signal processing by using a single set of measurement electronics.
Implementation Method 1
the controller measures the change in inductance of the plurality of wire coils caused by the position of the rotating structure relative to the plurality of wire coils
Implementation Method 2
each coil being coupled in parallel with a capacitor
Data Source
AI summary
A high sensitivity inductive sensor for measuring clearance of a rotating blade tip includes a one or more of sensing coils. The sensing coils are formed of magnet wire, which is wound to form planar spiral coils. Each of the coils are coupled in series with a function generator, which applies an excitation signal thereto. Accordingly, based on the change in impedance of the coils, a clearance measurement, which identifies the distance between the coil and the tip of the rotating blade can be obtained using predetermined calibration curve values.