One principal advantage of spinning probe eddy current instruments is:

The principal advantage of spinning probe eddy current instruments lies in their ability to locate the circumferential position of defects within the material being tested. This capability is particularly important in applications where defects may exist along the circumference of a component, such as pipes or tubing. The spinning action of the probe allows for a more comprehensive scan of the surface, enabling the operator to identify and map the position of defects accurately.

While other options may describe beneficial features of eddy current testing, the unique ability to determine the circumferential location is what sets spinning probe eddy current instruments apart. It is this precise defect positioning that enhances the effectiveness of inspections, especially in industries where structural integrity is critical.