Multi-Parameter eddy current measuring system with parameter compensation technical field
First Claim
1. A method of measuring physical parameters characteristic of a workpiece whose workpiece parameters include material, thickness, temperature, permeability and conductivity, said method comprising the steps of:
- providing an excitation circuit having electrical components that characterize system electrical parameters, said excitation circuit further having an excitation circuit impedance defined by said system electrical parameters;
providing said excitation circuit with a sensor having an electrical coil at a preselected diameter;
positioning said coil at a selected separation distance from said workpiece;
presenting said coil with an excitation signal at a single angular frequency selected such that an effective product of said workpiece permeability and resistivity and said separation distance map to a single point in an excitation circuit impedance plane;
measuring a voltage magnitude of said excitation signal;
measuring a phase of said excitation signal;
generating signals indicative of said single excitation circuit impedance plane point; and
generating signals indicative of a computed value of a desired one of said parameters.
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Accused Products
Abstract
This invention uses a single eddy current coil to measure multiple parameters of conductive target simultaneously using a single fixed frequency. For example, the system consisting of the sensor coil, connecting cable, and signal conditioning electronics, can measure the thickness of a target and the distance of the target from the coil. Alternatively, it could simultaneously measure the distance of the target to the coil, i.e. lift-off, and one of the electrical properties of the target, such as the resistivity. The present system is useful in material characterization of targets where the lift-off information can be used to correct for any lift-off induced error in the apparent resistivity. In general, it can determine any pair of two characteristics of the target/sensor relationship simultaneously. This invention provides significant improvement in accuracy and flexibility of eddy current sensors and can be manufactured at a low cost due to the use of a single coil and a single fixed frequency in the signal conditioning electronics. An alternative sensor configuration utilizing two sensors differentially to produce a cladding insensitive--displacement measurement is also contemplated by the present invention.
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Citations
21 Claims
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1. A method of measuring physical parameters characteristic of a workpiece whose workpiece parameters include material, thickness, temperature, permeability and conductivity, said method comprising the steps of:
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providing an excitation circuit having electrical components that characterize system electrical parameters, said excitation circuit further having an excitation circuit impedance defined by said system electrical parameters; providing said excitation circuit with a sensor having an electrical coil at a preselected diameter; positioning said coil at a selected separation distance from said workpiece; presenting said coil with an excitation signal at a single angular frequency selected such that an effective product of said workpiece permeability and resistivity and said separation distance map to a single point in an excitation circuit impedance plane; measuring a voltage magnitude of said excitation signal; measuring a phase of said excitation signal; generating signals indicative of said single excitation circuit impedance plane point; and generating signals indicative of a computed value of a desired one of said parameters. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A system for measuring physical parameters characteristic of a workpiece whose workpiece parameters include material, thickness, temperature, permeability and conductivity, said system comprising:
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an excitation circuit having electrical components that characterize system electrical parameters, said excitation circuit further having an excitation circuit impedance defined by said system electrical parameters; a sensor having a single electrical coil at a preselected diameter electrically connected to said excitation circuit; a means for positioning said coil at a selected separation distance from said workpiece; signal generator means for presenting said coil with an excitation signal at a single preselected angular frequency selected such that an effective product of said workpiece permeability and resistivity and said separation distance map to a single point in an excitation circuit impedance plane; a means for measuring a voltage magnitude of said excitation signal; a means for measuring a phase of said excitation signal; and processor means for generating output signals indicative of a desired one of said parameters. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification