Eddy current defect simulator and method

An eddy current inspection and calibration system comprising:

• a. an eddy current inspection system having a probe for producing electromagnetic fields for inducing eddy currents in a ferrous workpiece passing through the electromagnetic fields, said probe being responsive to changes in the fields caused by eddy current changes for enabling the inspection system to determine the presence of a defect in the workpiece,
• b. passive flaw simulator circuit means including variable impedance means inductively coupled to said probe for controllably varying the loading of the probe in a manner similar to variations caused by the introduction of a ferrous workpiece having a defect of a known severity into the electromagnetic fields, independently of the coupling to the probe of a portion of workpiece material.

A portable calibrating device usable with a probe assembly of an eddy current inspection system, for simulating a flaw in a ferrous workpiece having a defect of known severity, the calibrating device comprising:

• a. passive non-balanceable workpiece flaw simulator circuitry inductively couplable to a probe assembly and having a resistive component of impedance and an inductive component of impedance, for loading the probe to a first degree independently of coupling to the probe of a portion of workpiece material and,
• b. control means coupled to the workpiece flaw simulator circuitry for selectively varying the value of said resistive component for simulating the effect of a flaw in the ferrous workpiece.

Apparatus for simulating workpiece flaws in an eddy current inspection device for controllably varying loading of a detector probe of the eddy current inspection device, the apparatus comprising:

• a. electronic workpiece simulator circuitry electromagnetically couplable to said detector probe, said circuitry including impedance producing elements producing a resistive component and an inductive component operable to load said detector probe in a manner representative of the loading imposed by a defect-free ferrous workpiece independently of coupling to the probe of a portion of workpiece material;
• and,
• b. control circuitry coupled to said simulator circuitry for varying one of said components to produce a loading change on said detector probe representative of the loading change imposed by moving the probe from the region of an unflawed workpiece to the region of a ferrous workpiece having a defect of known severity.

In a method of calibrating nondestructive eddy current inspection apparatus without the aid of workpiece material, the steps of:

• a. electromagnetically coupling electronic workpiece simulator circuitry to a probe assembly of the inspection apparatus independently of coupling to the probe of a portion of workpiece material, the workpiece simulator circuitry providing an impedance having an inductive component and a resistive component, and,
• b. controllably varying the magnitude of the resistive component of the workpiece simulator circuitry in a predetermined manner to simulate defects in a ferrous workpiece.

An eddy current inspection system having apparatus for simulating a flaw in a workpiece for facilitating calibration of the eddy current inspection system, the system including a probe operable to produce electromagnetic fields for inducing eddy currents in the workpiece when present in the region of said fields, the probe being responsive to changes in impedance loading thereof caused by the presence of the workpiece in the field, the workpiece flaw simulator comprising:

• a first non-balanceable type of circuit means inductively couplable to said probe for impedance loading the probe to a first degree of impedance independently of coupling to the probe of a portion of workpiece material, and second circuitry connected to the first circuit means for altering the effective impedance of the first circuit means as seen by the probe to vary the impedance loading of the probe to simulate the introduction into the field of a ferrous workpiece having a flaw of a predetermined severity.