LVDT Sensor Phase Offset Evaluation for Magnetic Interference
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Solution Overview
Problem
Inductive sensors based on the LVDT principle face challenges in providing clear and reliable position detection due to ambiguity in measurement signals, especially in the presence of external magnetic fields and ferromagnetic materials, which can lead to distorted signals and increased circuit complexity.
Innovation Solution
The solution involves evaluating the phase offset between the output signals of the secondary coils to determine the position or change in position of the coupling element, allowing for robust and reliable operation independent of external interference, using a sensor with a primary coil and two secondary coils, and an evaluation device that processes these signals to generate a clear sensor output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amplitude modulation methods (full-wave rectification, synchronous demodulation) are used to evaluate sensor signals, then position detection is enabled, but circuit complexity increases and measurement clarity is reduced due to signal ambiguity
Solution Approach 1:
The patent replaces complex amplitude modulation evaluation circuits with a simple phase difference measurement approach. Instead of using full-wave rectification or synchronous demodulation circuits, the invention directly measures the phase offset between secondary coil signals, which naturally provides unambiguous position information without requiring complex electronics
Solution Approach 2:
The invention changes the evaluation parameter from amplitude modulation to phase difference measurement. By measuring the phase offset between the two secondary coil signals rather than their amplitudes, the system achieves clear position detection with simple electronics, as the phase relationship directly indicates coupling element position without ambiguity
2Reliability
If LVDT sensors are used in environments with external magnetic fields or ferromagnetic materials, then position measurement is performed, but signal distortion occurs leading to unreliable measurements
Solution Approach 1:
The patent replaces amplitude-based measurement (which is susceptible to magnetic interference) with phase-based measurement. The phase difference between secondary coil signals remains stable and unambiguous even in the presence of external magnetic fields or ferromagnetic materials, as phase relationships are not affected by signal amplitude variations caused by magnetic distortion
Solution Approach 2:
The invention uses a simple, robust evaluation method that does not require expensive shielding or complex interference compensation circuits. By relying on phase difference measurement, the system achieves reliable operation in magnetic environments without additional protective components or complex electronics
3Measurement precision
If separate full-wave rectification with difference formation is used to achieve clear characteristic curves, then measurement signal clarity is improved, but circuit complexity and cost increase
Solution Approach 1:
The patent substitutes complex separate full-wave rectification circuits with a simple phase difference measurement system. The phase offset between secondary coil signals directly provides clear position information without requiring rectification, demodulation, or difference formation circuits, achieving signal clarity with minimal electronics
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 enables clear and accurate position detection with high spatial resolution, unaffected by external magnetic fields, and reduces the complexity of the required electronics, making it suitable for environments with strong magnetic interference.
Implementation Method 1
The functional principle of inductive sensors that work according to the linear variable differential transformer (LVDT) principle is based on the coupling between a primary coil and two secondary coils by a coupling element
Implementation Method 2
A displacement of the coupling element has an influence on the voltages induced in the secondary coils, so that the position of the coupling element can be deduced from the voltages on the secondary coils
Data Source
AI summary
A sensor comprising a primary coil, two secondary coils, and an evaluation unit. An excitation signal (18) can be applied to the primary coil (12). An output signal (22a) or 22b, dependent on the position of a coupling element (16), can be induced in each secondary coil (14a and 14b). An evaluation unit (26) is configured to evaluate the output signals (22a and 22b) and to detect any phase shift between them. The evaluation unit (26) is further configured to provide a sensor output signal (28) indicating the position or a change in position of the coupling element (16).