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Rogowski Coil Current Transducers

In its simplest form a **Rogowski coil** is an evenly wound coil of **N** turns per metre on a non-magnetic former of constant cross sectional area **A**. The winding wire is returned to the starting point along the central axis of the former and the two ends are typically connected to a cable. The free end of the coil is normally inserted into a socket adjacent to the cable connection in a way that allows it to be unplugged thus enabling the coil to be looped around the conductor carrying the current to be measured.

An alternating or pulsed current in a conductor develops a magnetic field and the interaction of this magnetic field and the Rogowski coil local to the field gives rise to an induced voltage within the coil which is proportional to the rate of change of the current being measured. Provided the coil constitutes a closed loop with no discontinuities, it may be shown that the voltage **E** induced in the coil is proportional to the rate of change of the encircled current I according to the relationship **E=H.dI/dt**, where **H**, the coil sensitivity in (Vs/A), is proportional to **NA**.

To obtain an output voltage **V**_{OUT} proportional to **I** it is necessary to integrate the coil voltage **E**; hence an electronic integrator is used to provide a bandwidth extending down to below 1Hz.