Absolute property measurement with air calibration

Abstract

An instrument and method for providing accurate and reproducible measurement of absolute properties of a material under test without using conductivity or crack calibration standards. The instrument has a sensor designed to minimize unmodeled parasitic effects. To accomplish this, the sensor has one or more of the following features: dummy secondary elements located at the ends of a primary winding meandering, setting back of the sensing element from a connecting portion of the primary winding, or various grouping of secondary elements. The sensing elements of the sensor can be connected individually or in differential mode to gather absolute or differential sensitivity measurements. In addition, the instrumentation is configured such that a significant portion of the instrumentation electronics is placed as close to the sensor head to provide independently controllable amplification of the measurement signals therein reducing noise and other non-modeled effects.

Description

RELATED APPLICATIONS[0001]This application claims the benefit of provisional application 60 / 063,534, filed Oct. 29, 1997, provisional application 60 / 069,604 filed Dec. 15, 1997, and provisional application 60 / 104,526 filed Oct. 16, 1998, the entire teachings of are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]The technical field of this invention is magnetometry and, in particular, the nondestructive electromagnetic interrogation of materials of interest to deduce their physical properties and to measure kinematic properties such as proximity. The disclosed invention applies to both conducting and magnetic media.[0003]Conventional application of magnetometers, specifically eddy current sensors, involves the excitation of a conducting winding, the primary, with an electric current source of prescribed temporal frequency. This produces a time-varying magnetic field at the same frequency. The primary winding is located in close proximity to the material under test ...

AI Technical Summary

Benefits of technology

[0014]It is recognized that there is a need for measurement methods that provide estimates of the actual physical properties of the MUT Current techniques often measure “effective” properties that are only indirectly related to the actual physical properties (e.g., permeability and conductivity at a specified excitation frequency). These “effective” property measurements often provide insufficient characterization of the MUT For example, multiple temporal excitation frequencies are often used to obtain estimates of conductivity or permeability. This is not acceptable if these physical properties vary with temporal excitation frequency. In applications such as monitoring of aging and fatigue in ferrous and nonferrous metal alloys, it may be necessar

Problems solved by technology

These “effective” property measurements often provide insufficient characterization of the MUT For example, multiple temporal excitation frequencies are often used to obtain estimates of conductivity or permeability.

This is not acceptable if these physical properties vary with temporal excitation frequency.

Howev

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