Eddy Current Coating Thickness Measurement via Impedance Phase Rotation
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Solution Overview
Problem
Eddy current based coating thickness measurement methods are inadequate for substrates with varying conductivity, leading to errors in thickness determination due to changes in substrate and coating electrical conductivity during deposition processes.
Innovation Solution
The method involves determining a rotation angle to make the inductive reactance component of the impedance measurement insensitive to substrate conductivity, allowing for the establishment of a calibration curve that correlates inductive reactance with coating thickness, even when substrate conductivity changes, thereby minimizing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional eddy current measurement methods are used, then coating thickness can be measured on substrates with constant conductivity, but measurement accuracy deteriorates when substrate conductivity varies during deposition processes
Solution Approach 1:
The patent changes the measurement parameter from total impedance magnitude to the phase angle of impedance. The phase angle is determined by measuring the ratio of inductive reactance to resistance, which eliminates the influence of substrate conductivity variations. This parameter transformation allows accurate thickness measurement on substrates with varying conductivity during deposition processes.
Solution Approach 2:
The patent introduces an intermediate measurement approach by using the phase angle as a mediator between the eddy current signal and coating thickness. Instead of directly measuring impedance magnitude which is affected by substrate conductivity, the phase angle serves as an intermediary parameter that correlates with coating thickness while being insensitive to substrate conductivity changes.
2Ease of manufacture
If impedance magnitude is used for measurement, then the method is simple to implement, but measurement accuracy deteriorates due to sensitivity to substrate conductivity changes
Solution Approach 1:
The patent transforms the measurement parameter from impedance magnitude to phase angle by measuring the ratio of inductive reactance to resistance. This parameter change maintains implementation simplicity while eliminating sensitivity to substrate conductivity changes, thereby improving measurement accuracy without significantly increasing system complexity.
3Ease of operation
If calibration curves are established for constant conductivity substrates, then measurement is straightforward, but measurement accuracy deteriorates when substrate conductivity changes during deposition
Solution Approach 1:
The patent changes the calibration parameter from impedance magnitude to phase angle. The phase angle calibration curve is established based on the ratio of inductive reactance to resistance, which creates a calibration relationship that is insensitive to substrate conductivity changes. This allows straightforward operation while maintaining accuracy during deposition processes with varying conductivity.
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 accurate coating thickness measurement by reducing the impact of substrate conductivity variations, ensuring precise thickness determination even in applications where conductivity changes occur, such as in high-temperature deposition processes.
Implementation Method 1
Eddy current based techniques are typically used to measure the thickness of nonconductive coatings on nonmagnetic and conductive substrates. A coil of fine wire conducting an alternating current is used to set up an alternating magnetic field at the surface of the instrument's probe. When the probe is brought in contact with the surface of the coating, the alternating magnetic field will set up eddy currents on the surface of the conductive substrate.
Implementation Method 2
A coil of fine wire conducting an alternating current is used to set up an alternating magnetic field at the surface of the instrument's probe. When the probe is brought in contact with the surface of the coating, the alternating magnetic field will set up eddy currents on the surface of the conductive substrate.
Implementation Method 3
Electrical impedance, which is the total opposition that a circuit presents to alternating current, is used as a measure of the eddy current field strength. Electrical impedance, which is measured in ohms, includes three components—resistance, inductive reactance, and capacitive reactance.
Data Source
AI summary
A method of configuring an eddy current detector to measure a thickness of a coating on a substrate includes measuring an impedance of the coated substrate, and establishing an impedance plane plot using a computer. The method may also include determining a rotation angle. The rotation angle may be an angle of rotation of the impedance plane plot that will make the inductive reactance component of the impedance substantially insensitive to substrate electrical conductivity within a coating thickness range. The method may further include establishing a calibration curve that is substantially insensitive to substrate electrical conductivity using the rotation angle. The calibration curve may be a curve that relates the inductive reactance component of the impedance to coating thickness.