Differential Speed Sensor Arrangement for Noise Rejection
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Solution Overview
Problem
Existing speed sensor arrangements for turbomachines face challenges in accurately measuring the speed of rotation due to significant noise interference, which complicates the detection of perturbations caused by the rotating turbine or compressor wheels, making it difficult to determine the speed consistently.
Innovation Solution
A speed sensor arrangement featuring a first and second electrode configuration that share common mode noise, with the output being proportional to the difference between the two inputs, effectively rejecting common noise and allowing for accurate measurement of the speed of rotation by using a differential amplifier and a retaining member to secure the electrodes in position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single electrode is used to detect perturbations from the rotating wheel, then the speed measurement can be implemented, but the signal-to-noise ratio deteriorates due to significant noise interference from turbine rotation, electric fields, and electric currents
Solution Approach 1:
The single electrode is divided into two separate electrodes (first electrode and second electrode), each detecting signals from the rotating wheel. By segmenting the detection function, the system can process multiple signals and identify common noise components that affect both electrodes equally, thereby isolating the actual speed-related perturbations from the noise interference.
Solution Approach 2:
A differential amplifier is introduced as an intermediary device between the electrodes and the measurement system. This amplifier processes the signals from both electrodes differentially, enhancing the useful signal while suppressing common-mode noise. The differential amplifier acts as a mediator that separates the desired speed information from the harmful noise interference.
2Measurement precision
If electrodes are positioned close to the rotating wheel to detect perturbations, then the measurement sensitivity improves, but the exposure to harmful electric fields and noise increases
Solution Approach 1:
By using two electrodes instead of one, the system can spatially segment the detection points. Both electrodes are positioned close to the rotating wheel for high sensitivity, but their signals are processed differentially to cancel out the electric field interference that affects both locations similarly, thus maintaining sensitivity while reducing the impact of harmful fields.
Solution Approach 2:
The harmful electric field interference and noise that affect both electrodes are converted into a beneficial common-mode signal that can be rejected by the differential amplifier. The noise and interference, which would normally degrade the measurement, are transformed into a useful mechanism for identifying and eliminating unwanted signals, thereby improving the overall measurement quality.
3Object-affected harmful factors
If a differential amplifier is used to reject common mode noise, then the signal-to-noise ratio improves, but the device complexity increases with additional electrodes and circuitry
Solution Approach 1:
The detection function is segmented into two electrodes, which increases the complexity of the sensor arrangement. However, this segmentation enables the differential amplifier to reject common-mode noise, improving the signal-to-noise ratio. The benefit of noise rejection outweighs the cost of additional components, as the alternative (single electrode) cannot achieve effective noise cancellation.
Solution Approach 2:
The differential amplifier, while adding circuit complexity, serves as a necessary intermediary that enables common-mode noise rejection. Without this intermediary device, the system cannot effectively separate the useful signal from the harmful noise. The added complexity is justified by the significant improvement in measurement reliability and accuracy in noisy environments.
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 solution enhances the signal-to-noise ratio, enabling consistent and accurate measurement of the speed of rotation by isolating common noise, thus improving the reliability of the speed measurement in noisy environments.
Implementation Method 1
The perturbations may be, for example, perturbations in capacitance, or perturbations in charge accumulated at the electrode, or perturbations in an electric field
Implementation Method 2
perturbations in an electric field, for example, between the electrode and the turbine wheel
Implementation Method 3
an output arrangement, the output arrangement being configured to receive the first input and the second input, and to provide an output that is proportional to a difference between the first input and the second input
Data Source
AI summary
Sensor arrangement for measuring a rotation speed of a salient member of a rotatable body comprising a first electrode arrangement providing a first input, a second electrode arrangement providing a second input different from the first input, the first and second electrode arrangements configured so noise in the first and second inputs is substantially the same, and wherein variations in the first and second inputs are caused by rotation of the rotatable body and the salient member past the first and second electrode arrangements, an output arrangement for receiving the first and second inputs, and for providing an output proportional to a difference between the first and second inputs, and a retaining member for retaining one or more of the first and second electrode arrangements and output arrangement, the speed of rotation of the salient member measurable from a variation in the output caused by rotation of that salient member.