RT Series AC current sensors from LEM, Milwaukee, WI, offer better than 0.65% accuracy, including position error. The split-core Rogowski coils are suitable for use in Class 1 power devices and use a magnetic coupling technology to extend the magnetic flux at the loop opening, compensating for coil asymmetry. Features include exceptionally regular coil windings, a frequency range that includes 50/60 Hz, and an ultra-compact and flexible form. The sensor detects the rate of change of the primary current that induces a proportionate voltage at the terminals of the coil. An electronic integrator circuit converts the signal into an output proportional to the current in the primary circuit.