Non-Destructive Testing (NDT) Practice Test

How is the opposition to the primary magnetic field measured in eddy current inspections?

1. By using a thermal camera

2. By measuring the secondary field's strength

3. Via the eddy current instrument as an electrical signal

4. Through visual inspection techniques

The correct answer is: Via the eddy current instrument as an electrical signal

In eddy current inspections, the opposition to the primary magnetic field is effectively measured through the eddy current instrument, which generates an electrical signal in response to the presence and behavior of eddy currents in a conductive material. When an alternating magnetic field is applied via the probe, it induces eddy currents within the material being tested. The presence of flaws, changes in material properties, or variations in conductivity affects how these eddy currents circulate, thereby altering the secondary magnetic field that results from them. The eddy current instrument detects these changes and converts them into an electrical signal. This signal is then analyzed to determine the characteristics of the material, including any defects or anomalies. The relationship between the primary magnetic field and the induced eddy currents, as captured by the instrument, provides critical information on the material's integrity without causing any damage. Other methods mentioned, such as using a thermal camera or visual inspection techniques, do not measure the opposition to the primary magnetic field directly and are not suited for evaluating the specifics of eddy currents. Therefore, the choice of using the eddy current instrument to produce an electrical signal is central to this non-destructive testing technique.