# Principles of Eddy Current Conductivity Testing

Electrical conductivity is the measurement of a materials ability to conduct an electric current. This is the inverse of electrical resistivity, measuring a materials ability to resist an electric current.

Conductivity is widely used to indicate material type and determine the state of heat treatment. In order to give accurate readings the SigmaCheck uses a three-point reference method. The first measurement with the probe in the air and then two further measurements are required which span the range of interest.

Conductivity in metal is established using Ohm’s Law, which states that current through a conductor between two points, is directly proportional to the potential difference across the
two points. The resistance of the material, which is a constant for that material, allows the usual mathematical equation for this relationship to be true.