The high electrical conductivity of liquid metals permits the measurement of the surface position and shape of a melt in a container using the induction of eddy currents. An alternating ­magnetic field is applied and the resulting secondary ­magnetic field is measured using gradiometric induction coils.

Weakly and non-conducting inclusions, e.g. gas bubbles, distort an ­magnetic field in highly conducting liquid metals. The ­magnetic signature of the distortion can be measured and gives ­information on the size, shape, position and movement of the bubble.