An out of phase condition between current and voltage can exist in which part of an eddy current coil?

In an eddy current testing system, the concept of phase relationship between current and voltage is crucial for understanding how eddy currents are induced and detected. When alternating current is introduced into the coil (which serves as the primary winding), a magnetic field is created. This alternating magnetic field induces eddy currents in the conductive test specimen, creating a secondary effect.

The relationship between current and voltage phase in the primary winding is predominantly dictated by the inductive reactance. In an ideal case, the current lags behind the voltage due to this inductive reactance. Simultaneously, in the secondary winding, which is effectively influenced by the changes and induced eddy currents in the test specimen, a phase shift also occurs. As the eddy currents interact with the primary field, they cause variations in the back electromotive force (EMF), creating a unique phase relationship of delivery of the induced current relative to the excitation that is detected.

Since both the primary and secondary windings are integral to the eddy current testing operation, and due to the effects of inductance, changes in the test specimen, and the interactions between the current induced in the coil and the currents induced in the specimen (which are detected in the secondary), both windings can exhibit