Eddy Current Sensor Inductance Measurement via Frequency Detuning
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Solution Overview
Problem
Existing eddy current sensors face challenges in determining sensor coil inductance accurately due to interference from external electromagnetic signals, which can lead to incorrect angle measurements and electromagnetic compatibility issues, especially in far-range applications.
Innovation Solution
The method involves detuning the oscillation frequency of the LC oscillator circuit by adjusting the resonant capacitance or gate propagation time, allowing for precise determination of sensor coil inductance while minimizing the impact of interference signals, using a capacitor array or digital inverter with variable gate propagation time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the oscillation frequency is kept constant at resonant frequency for inductance measurement, then measurement simplicity is maintained, but interference signals cause incorrect frequency counting and measurement errors
Solution Approach 1:
The patent applies dynamics by making the oscillation frequency variable rather than constant. The frequency is dynamically adjusted during the measurement process - starting at the resonant frequency and then being shifted away from it. This dynamic frequency adjustment allows the system to avoid being locked onto interference signals while completing the inductance measurement, thereby resolving the contradiction between measurement simplicity and interference rejection.
Solution Approach 2:
The patent implements periodic action through the time-dependent frequency modulation process. The measurement is performed in periodic cycles where the frequency is first set to resonant frequency for accurate inductance determination, then deliberately shifted away from resonance to avoid interference signal locking. This periodic modulation of frequency prevents continuous exposure to interference while maintaining measurement accuracy.
2Object-affected harmful factors
If the oscillation frequency is detuned during measurement, then interference signal influence is reduced, but measurement complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the oscillation frequency parameter during the measurement process. The frequency is changed from the resonant frequency to a non-resonant frequency in a controlled manner. This parameter modulation is achieved through simple frequency shifting mechanisms that do not require complex additional hardware, thus reducing interference influence while maintaining acceptable device complexity.
3Object-affected harmful factors
If loops with different winding senses are used to compensate magnetic fields, then electromagnetic compatibility is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the interference compensation function from the physical coil structure and transfers it to the frequency control domain. Instead of modifying the coil winding pattern to cancel magnetic fields, the solution extracts the problem to the electrical domain by using frequency modulation to avoid interference signals. This approach maintains simple coil design while achieving electromagnetic compatibility through frequency management.
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 ensures stable and precise operation of eddy current sensors by reducing the influence of interference signals on inductance measurement, enhancing electromagnetic compatibility and frequency stability without complex adaptations to the sensor coil design.
Implementation Method 1
an inductance is determined by measuring and integrating an oscillating frequency of an LC oscillator circuit, the oscillating frequency being dependent on the inductance
Implementation Method 2
A voltage is induced in a simple spiral coil that is exposed to an alternating magnetic field
Implementation Method 3
The coil system is excited with a high-frequency signal, which causes simple spiral coils to emit electromagnetic fields
Implementation Method 4
A voltage is induced in a simple spiral coil that is exposed to an alternating magnetic field, which can have a negative interaction with the sensor electronics
Data Source
Figure 1
Figure 2A~2D
Figure 3A~3D
AI summary
The invention relates to a method for determining a sensor coil inductance of an eddy current sensor (2) by means of a LC-oscillator circuit (3), wherein the sensor coil inductance is determined by integration as a function of an oscillation frequency (fLc) and a resonant capacitance of the LC-oscillator circuit (3). It is provided that during the integration the oscillation frequency (fLc) is detuned at least once.