Capacitive Sensor for Turbomachine Blade Vibration
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Solution Overview
Problem
Existing methods for determining the vibratory modes of turbine engine rotor blades are limited by sensitivity to fouling, measuring precision, and the need for powerful computing resources, and cannot detect vibrations when all blades move in concert.
Innovation Solution
Measuring the minimum distance between sensors and the tip of each blade along a radial axis to calculate variations in length, which are used directly to model deformation and deduce vibratory modes, reducing the reliance on passing time measurements and processing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical probes are used for measuring blade passing time, then measurement precision is improved, but sensitivity to fouling increases
Solution Approach 1:
The patent replaces optical measurement systems with capacitive sensors that use electrical fields instead of light. The capacitive sensor detects blade passage through changes in capacitance caused by the conductive blade moving through the sensor's electrical field, eliminating the optical path vulnerability to fouling while maintaining measurement capability.
Solution Approach 2:
The patent introduces an electrical field as an intermediary between the sensor and the blade. The capacitive sensor creates an electrical field that interacts with the conductive blade, allowing indirect detection of blade position and vibration without direct optical contact, thus avoiding fouling issues.
2Reliability
If Foucault current sensors are used for measuring blade passage, then robustness to fouling is improved, but measurement precision deteriorates
Solution Approach 1:
The patent modifies the sensor signal processing by focusing on the derivative (rate of change) of the capacitive signal rather than the absolute signal level. This parameter transformation sharpens the measurement threshold, converting the gradual Foucault-like signal into a precise timing indicator based on the maximum rate of change, thereby recovering precision while maintaining fouling robustness.
3Measurement precision
If Tip-Timing method is used to determine blade vibrations, then vibration detection capability is improved, but device complexity and processing requirements increase
Solution Approach 1:
The patent extracts and measures only the specific parameter needed for vibration detection—the minimum distance between sensor and blade tip—rather than processing the entire passing time signal. By focusing on this single critical measurement point, the system simplifies the data processing requirements while maintaining vibration detection accuracy.
Solution Approach 2:
Instead of measuring the time for the blade to pass the sensor and inferring position from that time measurement, the patent directly measures the spatial parameter (minimum distance) and uses that directly for vibration analysis. This inversion of the measurement approach eliminates the need for complex time-to-position conversion algorithms.
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
This approach enhances measurement robustness and precision, allows detection of vibrations even when all blades move simultaneously, and reduces the need for large and costly processing units, while refining the determination of vibratory modes by combining radial deformation and passing time variations.
Implementation Method 1
The sensor is a sensor capable of measuring a distance at the blade tip, such as a capacitive sensor
Data Source
AI summary
A method for determining the vibration of turbomachine rotor blades, including steps of measuring, via one or more sensors, the variation in the minimum distance between each sensor and the top of each blade along a radial axis of the rotor, between successive rotations of each blade in front of each sensor, a minimum distance value being obtained on each passage of each blade in front of each sensor, in order to deduce therefrom a variation in the lengths of the blades along the radial axis; and, using directly, as such, the variation in the length of the blades along the radial axis in a model of the deformation of the blades, in order to deduce therefrom characteristics of one or more vibrational modes of the rotating blades. A turbomachine can be equipped with a device implementing this method.