Plural coil eddy current mapping probe

摘要

An eddy current probe for mapping holes within a tube sheet of a steam generator, having a first coil (12) positioned at the top of the probe (10) with its axis coincident with the axis of the probe. A first coil pair (14 and 16) is arranged along a common axis perpendicular to the axis of the probe below the first coil (12) and is situated a distance from and on either side of the axis of the probe. A second pair of eddy current coils (18 and 20) is positioned along a common axis perpendicular to the axis of the probe and the axis of the first coil pair with the respective coils of the second pair located on either side of and spaced from the probe axis. Each of the respective coils are arranged to be separately excited by an alternating current source with the respective coil pairs coupled in opposition in corresponding balanced bridge arrangements. Means are provided for indicating a variation in the impedance of the first coil and an imbalance in either of the separate bridge arrangements of the first and second coil pairs.