Which of the following statements best describes the selection of eddy current test frequency?

The correct response emphasizes that there is a range of suitable frequencies centered around an optimum frequency for conducting eddy current testing. This approach acknowledges that while a specific frequency may yield the best results for a given application, several nearby frequencies can still provide reliable and relevant information for evaluating the material or component being tested.

The concept of having a range around the optimum frequency allows for variations in factors such as material conductivity, geometry, and surface conditions, which can affect eddy current responses. By focusing on a band of frequencies, inspectors can account for these variables and still achieve effective detection of flaws or material properties.

In terms of the other options, stating that the frequency must equal or be a tight percentage around a specific ratio could limit flexibility and effectiveness in a field where variations occur naturally. Furthermore, specifying a ±25% range might be too broad for some applications, reducing sensitivity and test resolution. Overall, understanding the importance of frequency selection within a defined range is crucial for optimizing the performance of eddy current testing.