Multi-Frequency Eddy-Current Thickness Measurement Without Complex Calibration
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Solution Overview
Problem
Existing eddy-current thickness measurement methods are not suitable for industrial applications due to variability in measurement conditions, requiring lengthy calibration procedures and high measurement times, leading to inaccuracies in estimating thickness, especially for thin laminates.
Innovation Solution
A thickness measuring device using a multi-frequency excitation signal and polynomial interpolation to estimate thickness, eliminating the need for complex calibration and reducing measurement time while maintaining accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional eddy-current measurement methods are used, then non-contact thickness measurement is achieved, but measurement time becomes excessively long and calibration procedures become complex
Solution Approach 1:
The patent applies parameter changes by using multi-frequency excitation signals instead of single-frequency signals. The system measures impedance at multiple frequencies (e.g., 5-10 frequencies across a range) and uses polynomial interpolation to determine the characteristic frequency. This approach maintains measurement accuracy while significantly reducing calibration complexity and measurement time compared to traditional single-frequency methods.
2Measurement precision
If traditional eddy-current measurement methods are used, then non-contact thickness measurement is achieved, but calibration procedures become complex and time-consuming
Solution Approach 1:
The patent implements self-service by enabling the measurement system to automatically determine the characteristic frequency through polynomial interpolation of multi-frequency impedance measurements. The system performs self-calibration by fitting a polynomial to the measured impedance data across multiple frequencies and automatically identifying the characteristic frequency without requiring manual calibration procedures or reference measurements, thereby eliminating complex calibration steps.
3Productivity
If polynomial interpolation with multi-frequency excitation is used, then measurement time is reduced and calibration is simplified, but measurement accuracy for thin laminates must be maintained
Solution Approach 1:
The patent applies partial action by using a limited set of discrete frequency points (e.g., 5-10 frequencies) rather than continuous frequency sweeping. The polynomial interpolation method estimates the characteristic frequency from these partial measurements, achieving sufficient accuracy for thin laminate measurement without requiring exhaustive frequency analysis, thus balancing speed and precision.
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
Enables fast and accurate non-contact thickness measurement of non-magnetic materials without prior knowledge of nominal thickness, suitable for industrial use.
Implementation Method 1
the principle of operation of an eddy-current measurement consists in the use of a coil which, excited by an alternating electrical signal, induces eddy currents in the conductive object under test
Implementation Method 2
induces eddy currents in the conductive object under test. The excitation coil itself or another coil (denoted as detection or pickup coil) measures the reaction magnetic field due to the eddy currents
Data Source
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AI summary
A thickness measuring device (1) for measuring thickness of a non-magnetic conductive object (5), entails: an eddy-current sensor stage (2), having a coil element (4) to be arranged at a given distance (d) from the object (5) and an excitation module (2a), which provides an excitation signal (Sin) to the coil element (4) in order to generate eddy currents; and a processing stage (40), which processes detection signals (Sd) provided by the coil element (4) as a function of the magnetic field generated by the eddy currents in order to estimate a thickness (c) of the object (5). The processing stage (40) estimates the thickness (c) as a function of a peak frequency (fmin) associated with an impedance variation occurring when the coil element (4) is arranged near the object (5) as compared to when the coil element (4) is placed in air and as a function of a characteristic variable (α0) associated with the coil element (4) and with the object (5). In particular, the processing stage (40) implements an optimization module (16), to calculate an optimized value for the characteristic variable (α0) and a thickness estimation module (18), to estimate a corresponding value of the thickness (c).