Rogowski coil

The Rogowski coil is an electrical device for measuring alternating current (AC). It consists of a helical coil of wire with the lead from one end returning through the centre of the coil to the other end, so that both terminals are at the same end of the coil. The whole assembly is then wrapped around a straight conductor. A voltage is induced in the coil proportional to the rate of change of current in the straight conductor.

One advantage of a Rogowski coil over other types of induction coil is that it can be made open-ended and flexible, allowing it to be wrapped around a live conductor without disturbing it. Since a Rogowski coil has an air core rather than an iron core, it has a low inductance and can respond to fast-changing currents. Also, because it no iron core to saturate, it is highly linear even when subjected to large currents, such as those used in electric power transmission and welding. A correctly formed Rogowski coil, with equally spaced windings, is largely immune to electromagnetic interference.

A device similar to the Rogowski coil was described in "On a magnetic potentiometer", Philosophical Magazine and Journal of Science, vol. XXIV, no. 5th Series, pp. 94–96, Jul-Dec 1887, by A. P. Chattock of Bristol University, who used it to measure magnetic fields rather than currents. The definitive description was given by W. Rogowski and W. Steinhaus in "Die Messung der magnetischen Spannung", Archiv für Elektrotechnik, 1912, 1, Pt.4, pp.141-150.