Speed Sensor for Rotating Member Using Electric Field Perturbation
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Solution Overview
Problem
Capacitive sensors used in turbomachinery face challenges with low signal-to-noise ratios and interference from contaminants and thermal expansion, making it difficult to accurately measure rotational speed in noisy engine environments.
Innovation Solution
A speed sensor that uses a constant voltage source to generate an electric field, detecting current flow modulated by the rotation of a salient feature within the field, with an amplifier circuit to enhance the signal and shielded components to reduce noise, allowing for precise measurement of rotational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor is used to measure rotational speed in turbomachinery, then the sensor can detect speed changes, but the signal-to-noise ratio becomes very low due to electrical noise in the engine environment
Solution Approach 1:
The patent replaces the conventional capacitive sensing method with a magnetic field-based sensing approach. Instead of using electrical capacitance changes to detect rotational speed, the invention uses a magnetic sensor to detect changes in magnetic field caused by the rotation of the turbine wheel, thereby avoiding the electrical noise problems that plague capacitive sensors in engine environments.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the sensor and the rotating member. The magnetic sensor detects changes in the magnetic field caused by the rotation of the turbine wheel, using the magnetic field as a mediator to transfer information about rotational speed without direct electrical contact, thus isolating the sensing system from electrical noise.
2Measurement precision
If the separation between the sensor electrode and the turbine wheel is minimized to increase capacitance signal, then measurement sensitivity improves, but mechanical construction and thermal expansion requirements cannot be met
Solution Approach 1:
The patent replaces the capacitive sensing mechanism that requires minimal separation distances with a magnetic sensing mechanism. The magnetic sensor can accurately detect rotational speed changes over larger separation distances, eliminating the need to compromise mechanical tolerances and thermal expansion allowances for the sake of signal strength.
Solution Approach 2:
The patent changes the fundamental sensing parameter from electrical capacitance to magnetic field detection. This parameter change allows the sensor to operate effectively at larger separation distances from the turbine wheel, accommodating mechanical construction requirements and thermal expansion without sacrificing measurement sensitivity.
3Measurement precision
If capacitive sensors are used in turbomachinery, then speed measurement is possible, but the sensors are adversely affected by contaminants in the gas and deposits on the electrode
Solution Approach 1:
The patent replaces the capacitive electrode-based sensing system with a magnetic field-based sensing system. This substitution eliminates the exposed electrode that is vulnerable to contaminant deposits, as the magnetic sensor can detect rotational speed through changes in the magnetic field without requiring direct exposure to the gas flow and contaminants.
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 solution provides improved signal-to-noise ratios and robustness against contaminants and thermal changes, enabling accurate measurement of rotational speed in turbomachinery despite challenging environmental conditions.
Implementation Method 1
a current detector for detecting current flow between the constant voltage source and the electrode due to perturbation of the electric field by passage of at least one salient feature of the rotating member through the electric field as the rotating member rotates
Data Source
AI summary
A speed sensor for use in measuring the speed of rotation of a rotationally salient rotating member. The speed sensor comprises an electrode and a sensor circuit. The sensor circuit comprises a constant voltage source for supplying a voltage to the electrode to generate an electric field in a dielectric medium. A current detector detects current flow between the constant voltage source and the electrode due to perturbation of the electric field by passage of at least one salient feature of the rotating member through the electric field as the rotating member rotates. The current detector outputs a first signal modulated at a frequency corresponding to the frequency of perturbation of the electric field. The first signal is amplified to produce an amplified signal modulated at a frequency corresponding to the frequency of perturbation of the electric field.