LVDT/RVDT Phase-Shift Sensing for Faster Position Feedback
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Solution Overview
Problem
Linear and rotary variable differential transformers (LVDT/RVDT) systems require six cables, leading to large wire bundles, noise issues, and measurement inaccuracies due to relative errors in sensing coils, and incur delays from RMS voltage measurement processing.
Innovation Solution
The use of pseudo-loads with different impedance characteristics connected to LVDT/RVDT systems to induce phase-shifts in signals, allowing for remote detection of object movement with fewer cables, reducing weight and space requirements, and eliminating the need for averaging circuits for faster position determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If six cables are used to connect all three coils (excitation coil and two sensing coils), then complete signal transmission is achieved, but wire bundle size and noise increase
Solution Approach 1:
The patent extracts the excitation coil connection from the cable bundle by providing the excitation signal through a separate path (e.g., through the movable object or via a different routing), leaving only the two sensing coils connected via cables. This reduces the number of cables from six to four, decreasing wire bundle size and associated noise while maintaining complete signal transmission capability.
2Reliability
If six cables are used to connect all three coils, then complete signal transmission is achieved, but measurement accuracy decreases due to relative errors in sensing coils
Solution Approach 1:
The patent combines the signals from the two sensing coils through a differential measurement approach, where the output is derived from the difference between the two sensing coil signals. This merging technique inherently compensates for common-mode errors and relative variations in the sensing coils, improving measurement accuracy while maintaining complete signal transmission.
3Reliability
If RMS values are used for voltage measurements, then measurement robustness is improved, but measurement delay increases due to filtering process
Solution Approach 1:
The patent replaces the traditional RMS measurement method with a phase-difference based measurement approach. Instead of computing RMS values that require filtering and averaging operations, the system measures the phase difference between the excitation signal and sensing coil signals directly. This substitution eliminates the time-consuming filtering process while maintaining measurement robustness through phase-based detection.
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 reduces the number of cables needed, minimizes noise and measurement errors, and provides faster position feedback by using phase-shift sensing circuits to determine object movement, enhancing the accuracy and efficiency of LVDT/RVDT systems in applications like rocket systems.
Implementation Method 1
An excitation signal is generated on one or both of the sensing coils depending upon the position of the core
Implementation Method 2
When the core is aligned between the excitation coil and the first sensing coil, the excitation signal shows up on the first sensing coil and not the second sensing coil
Data Source
AI summary
A representative phase-shift based method for using a transformer system to detect movement of an object, and associated systems and methods are disclosed. A representative transformer system detects movement of an object and includes an excitation coil configured to receive an excitation coil input signal that results from an input sinusoidal signal. The transformer further includes first and second sensing coils, and a core configured to be operatively coupled to the object. The core moves relative to the first and second sensing coils when the object moves. First and second impedance loads are connected to the first and second sensing coils, respectively. The two impedance loads have different phase-shifting characteristics. A phase-shift sensing circuit determines a phase-shift between the excitation coil input signal and the input sinusoidal signal that is correlated with a position of the core relative to the first and second sensing coils.