Magnetic flux density as a probe of the state of electrical contacts

A new remote measuring technique for electrical contacts has been developed and tested in laboratory experiments. By measuring variations in the magnetic flux density outside an electrical contact, the current distribution in the contact region can be probed. At the contact interface the current is constricted to a limited number of contact spots, a-spots. If the condition of an electrical contact is good, a large number of a-spots are evenly distributed over the contact interface. As the contact degrades the number of contact spots decreases and statistically the distribution of a-spots over the contact interface will be more inhomogeneous. The laboratory tests clearly show how an inhomogeneous current distribution develops in the vicinity of a contact interface where the contact spots are unevenly distributed. The inhomogeneities have been resolved up to a distance of 35 mm away from the contact interface.