what is a rogowski coil
A Rogowski coil is a toroid of wire used to measure an alternating current i(t) through a cable encircled by the toroid. The above picture shows a coil encircling a current-carrying cable, with its output terminals v(t) connected to an integrator circuit, to obtain a voltage Vout(t) proportional to i(t) .t 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.