US 5,541,510 A · Multi-Parameter eddy current measuring system with parameter compensation technical field

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.

Claims21

Dependent claims

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.

6 more elements

A system for measuring physical parameters characteristic of a workpiece whose workpiece parameters include material, thickness, temperature, permeability and conductivity, said system comprising:

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.

5 more elements

Dependencies are inferred from the claim text.

Multi-Parameter eddy current measuring system with parameter compensation technical field

Life of this patent

Multi-Parameter eddy current measuring system with parameter compensation technical field

Life of this patent

Abstract

Claims21