What is the primary purpose of the secondary winding in an eddy current coil?

The primary purpose of the secondary winding in an eddy current coil is to detect changes in the eddy current flow induced in the test specimen. When the primary winding of the coil generates an alternating magnetic field, it induces eddy currents within the conductive test material. The secondary winding is crucial as it acts as a sensing element, measuring the resulting changes in the magnetic field due to these induced eddy currents.

Changes in the test specimen, such as variations in conductivity, thickness, or the presence of cracks, will affect the eddy currents. The secondary winding detects these variations by measuring the impedance change in the coil, allowing for assessment of the material's integrity. This response forms the basis for nondestructive testing, where the relationship between the induced currents and the properties of the test material is analyzed for evaluation purposes.

While inducing eddy currents is a vital function of the primary winding, the secondary winding specifically focuses on sensing and indicating any variations that occur in the generated eddy currents, which directly correlates to the condition of the test specimen.