Henry W Gruber

US Patent:

42075203, Jun 10, 1980

Filed:

Apr 6, 1978

Appl. No.:

5/893869

Inventors:

John H. Flora - Lynchburg VA
Henry T. Gruber - Columbus OH

Assignee:

The United States of America as represented by the Secretary of the Air
Force - Washington DC

International Classification:

G01R 3300

US Classification:

324238

Abstract:

An apparatus for inspecting for cracks under installed fasteners and the like using a multiple frequency digital eddy current system. A computer with a plurality of digital arrays generate drive signals which are converted to analog and applied to the test coil, a second set of digital arrays generate balance signals, are adjusted in amplitude and phase and drive signals so that the output of the test coil is zero in a test specimen, output signals from a work piece are processed in the computer giving phase-sensitive crack detection.