Abstract: A ferromagnetic eddy current probe apparatus having a double shielded magnetic coil to reduce the size of the magnetic filed and to generate a sharply focused electromagnetic field. A ferromagnetic steel alloy provides a double shield effect for greater concentration of the electromagnetic field onto a test specimen, and also to prevent probe tip wear and deformation when used to inspect fastener holes with a high speed designed feature maintenance the size setting of the probe (coil-end) diameter. An expansion slot in the end of the probe provides a spring action during probe radiation to keep a constant contact with the wall of a fastener hole. The ferromagnetic probe portion is removeable from the shank-end (a non-metallic portion of the probe) for easy repair or replacement and provides electrical isolation to prevent shorting of the signal.

Abstract: An eddy current probe calibration standard for calibrating eddy current probes and instruments utilizing calibration discs that provide a standard defect of known dimensions to produce a known repeatable signal. A plurality of round discs with different diameter holes through their centers are respectively provided to accommodate different size probes. Each disc has a defect in the wall of the hole in the form of a slot with known dimensions which will reproduce a known, repeatable signal. A flat, rectangular block which supports the discs, contains surface slots of known dimensions to produce known, repeatable signals for calibration when testing for surface defects.

Abstract: An automatic eddy current probe is revolved in a hole to be inspected, the output of the probe is divided to provide two signals to a recorder, a filtered signal will indicate the presence or absence of a flaw, a non filtered signal indicates probe position, this is particularly valuable when scanning through several structural layers.

Abstract: An eddy current flaw detector is held in a mounting block by a spring bias, the mounting block is selectively rotatable about a shank member for varying the radius of the detector as the shank rotates about a pivot point, turned by an electric drive mechanism.