What is the main advantage of using direct current in magnetic particle testing over alternating current?

Using direct current in magnetic particle testing has the primary advantage of its ability to detect smaller defects compared to alternating current. Direct current establishes a constant magnetic field which can create a stronger and more stable indication of flaws. This stability is crucial when trying to identify smaller defects that may not be as easily detectable with the fluctuating magnetic field of alternating current.

In alternating current, the magnetic field periodically reverses, which can lead to a phenomenon known as particle repulsion. This can obscure the indications of defects, particularly if the defects are small or located in areas where the magnetic field might fluctuate significantly. On the other hand, the steady nature of direct current minimizes this issue and allows for a clearer visualization of defects through visible magnetic particle indications.

Additionally, while other options may have benefits in different contexts, such as improving the overall speed of testing or enhancing safety measures, those do not directly relate to the improved defect detection capabilities that direct current offers compared to alternating current.