Passive Eddy Current Sensor Differential Circuit for Gas Turbine
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Solution Overview
Problem
Passive eddy current sensors used in gas turbines face challenges with electromagnetic interference noise and temperature limitations, which affect their ability to accurately sense blade rotation and clearance, especially in harsh environments with high temperatures and electromagnetic radiation.
Innovation Solution
A system utilizing two passive eddy current sensors with circuitry that combines their outputs to cancel common mode electromagnetic interference noise, allowing the sensors to operate effectively in high-temperature environments without the need for active cooling, by using silicon-on-insulator substrates for high-temperature amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive eddy current sensors are used to sense blade rotation and clearance in gas turbines, then sensing capability is provided, but electromagnetic interference noise degrades measurement precision
Solution Approach 1:
The patent applies differential measurement technique where two sensors are positioned to experience the same electromagnetic interference noise. By subtracting the two sensor outputs, the common-mode EMI noise cancels out while the actual blade proximity signal is preserved. This converts the harmful EMI into a cancelable common-mode signal, improving measurement precision without requiring shielding or filtering that would complicate the system.
2Ease of operation
If electronics are located in proximity to passive eddy current sensors for signal processing, then signal processing capability is provided, but high temperatures exceed electronics operating limits
Solution Approach 1:
The patent separates the sensing function from the signal processing function by placing the passive eddy current sensors in the high-temperature environment near the turbine blades while locating the active electronics in a cooler remote location. The sensors generate voltage signals that can be transmitted through wiring to the remote electronics for processing, allowing the system to maintain signal processing capability while protecting electronics from excessive heat.
3Productivity
If multiple wire connections are used between sensor coils, then electrical connections are provided, but combined resistance and inductance reduce sensor bandwidth
Solution Approach 1:
The patent combines the outputs of two passive eddy current sensor coils using a differential connection scheme. By connecting the coils in a differential configuration and subtracting their outputs, the system achieves EMI noise cancellation while maintaining adequate bandwidth. The merging of the two sensor signals through differential processing allows the system to overcome the bandwidth limitations that would result from individual coil connections.
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 effectively eliminates electromagnetic interference noise and operates reliably at temperatures exceeding 125°C, enabling accurate sensing of blade proximity and speed without active cooling, thereby improving gas turbine engine control.
Implementation Method 1
a passive eddy current sensor (or other suitable proximity sensor) positioned to sense blade rotation and blade-shroud clearance can be used to modify the engine operation
Implementation Method 2
When a blade passes through the magnetic field, eddy currents form in the blade material and the local magnetic field shifts, producing a voltage potential across the leads of the coil
Implementation Method 3
The circuitry combines the outputs of the first and second coil-wound cores so that common mode signals thereof subtract from each other to eliminate from the output signals of the circuitry any electromagnetic interference noise present in the outputs of the first and second coil-wound cores
Data Source
AI summary
A system and method for sensing the periodic proximity of one or more objects, such as the rotating blades of a gas turbine. The system includes a passive eddy current sensing unit having first and second magnets and first and second coil-wound cores coupled to generate and detect first and second magnetic fields. The sensing unit is positioned relative to the object such that the first and second coil-wound cores produce outputs in response to the object periodically passing through the first and second magnetic fields, respectively. Circuitry electronically combines the outputs of the first and second coil-wound cores to produce output signals corresponding to the proximity and timing of the object as it periodically passes through the first and second magnetic fields. Electromagnetic interference noise present in the outputs of the first and second coil-wound cores is eliminated from the output signals of the circuitry.