Coating Thickness Measurement Using Eddy Current Frequency Difference
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Solution Overview
Problem
Existing methods for measuring the thickness of conductive coatings on non-magnetic substrates, such as titanium, are either imprecise or unsuitable, particularly for cylindrical surfaces and conductive coatings like tungsten carbide, as they fail to provide individual thickness measurements or are affected by the substrate's magnetic properties.
Innovation Solution
A method using induction means to supply alternating electrical signals and measure physical characteristics like impedance at different frequencies, calculating the difference in these measurements to determine the coating thickness, which correlates with predetermined data for precise evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic permeability measurement is used to measure coating thickness, then measurement can be performed on the coating, but the method cannot be used when the substrate is non-magnetic because the magnetic field is not disturbed by the substrate
Solution Approach 1:
The patent changes the measurement parameter from magnetic permeability to electrical conductivity. By using eddy current measurement principles, the system measures the electrical conductivity of the coating material rather than magnetic properties, enabling measurement on non-magnetic substrates like titanium while maintaining measurement capability on the coating layer.
2Measurement precision
If eddy currents are used to detect coating thickness on conductive substrates, then measurement is possible, but the precision is insufficient
Solution Approach 1:
The patent segments the measurement into two distinct conductivity measurements: one for the coating layer and one for the substrate. By measuring the conductivity of each layer separately and using their difference, the system achieves precise thickness measurement on conductive coatings while eliminating interference from the conductive substrate.
Solution Approach 2:
The patent introduces the concept of equivalent conductivity as an intermediary parameter. Instead of directly measuring thickness, the system measures the equivalent conductivity of the coating-substrate system, then derives thickness from the difference between this equivalent conductivity and the substrate conductivity, providing more reliable measurements on conductive materials.
3Ease of operation
If geometry measurements are used to measure coating thickness on cylindrical surfaces, then diameter measurement is simple, but individual thickness values on different sides cannot be determined
Solution Approach 1:
The patent replaces mechanical geometry measurement with electromagnetic field measurement. By using eddy current probes that can be positioned at different locations on the cylindrical surface, the system measures electrical conductivity at each point and calculates individual thickness values, providing both ease of operation and precise local thickness measurement on complex geometries.
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 allows for precise and non-destructive measurement of coating thickness on conductive substrates, simplifying calculations and improving precision, especially for coatings on complex shapes like cylindrical surfaces.
Implementation Method 1
supplying induction means with at least one alternating electrical signal in order to induce in the part a magnetic field dependent on the electrical signal power supply
Implementation Method 2
measurement using Eddy Currents generated in the substrate when the coatings are non-conductive and the substrate is itself conductive
Implementation Method 3
measuring at least one physical characteristic varying as a function of the magnetic field induced in the part
Data Source
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AI summary
The invention relates to a method for measuring the thickness of a coating layer (Rev) of a part (P) that is formed on a substrate (Sub) of said part. The method comprises: supplying power to an induction means (Mind) using an AC electrical signal (S) in order to induce a magnetic field in the part (P); measuring at least one physical characteristic (Zn) that changes on the basis of the magnetic field (B) induced in the part (P); determining a first and second value of an indicator, which are determined from measurements of said physical characteristic that is produced when the electrical signal has first and second given frequencies, respectively; and then calculating the difference between the first and second value of the indicator, and determining the thickness (er) of the coating layer in accordance with said difference and with predetermined data that correlate the difference between values of the indicator with corresponding values of the thicknesses of the coating layer.