1. n. []

An in-situ measurement of the inside diameter of a casing or tubing using an electromagnetic technique. As with the electromagnetic thickness measurement, and usually measured at the same time, a coil centered inside the casing generates an alternating magnetic field. Another coil farther up the tool measures the phase shift introduced by the casing. At high frequency, the signal penetrates less than a tenth of a millimeter into the casing, and the phase shift can be related to the casing internal diameter. Unlike a mechanical or ultrasonic caliper, the measurement does not respond to nonmagnetic scale. For the purpose of determining the true internal diameter, this is a disadvantage, but for the purpose of determining corrosion, it is an advantage.

See related terms: casing-inspection log,  casing-potential profile,  electromagnetic thickness,  inside diameter,  multifinger caliper,  phase shift,  ultrasonic caliper