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Coil sensors deliver accuracies of 0.65%

16 October, 2009

The Swiss electrical measurements specialist LEM has announced a new type of Rogowski coil sensor that, it claims, will achieve accuracies of better than 0.65%, regardless of the position of the conductor. The RT sensors, based on a patent-pending development called Perfect Loop Technology, are the first split-core Rogowski coils that are suitable for use in Class 1 power monitors and energy meters.

In conventional split-core Rogowski coils, the discontinuity at the opening results in an asymmetry which can lead to an unbalanced geometry and makes the coil more sensitive to the position of the monitored conductor, and to external electric cables.

Some manufacturers use complex, costly clasp designs to minimise the effects of this discontinuity, but LEM claims to have invented a unique magnetic coupling technology that allows the magnetic flux to expand perfectly over the loop opening, thus compensating for any asymmetries. In addition, an advanced coil-winding process results in extremely regular windings, further enhancing the sensor’s symmetry, accuracy and immunity to electromagnetic interference. 

Sensors based on conventional Rogowski coils combine an almost perfect linearity with no saturation or upper limit in the current rating, and a wide frequency range, in a compact, flexible form. LEM says that its RT sensors (below) retain these benefits while overcoming the susceptibility to asymmetry and minimising unevenness in the coil winding.

The thin, light and flexible RT sensors can be fitted into applications in which traditional current transformers would be too heavy and bulky, especially when measuring high currents. Their split-core construction allows them to be wrapped around a conductor without dismantling cables or shutting down operation. 

The self-powered, 5mm-gauge sensors are available with 55mm or 125mm sensing aperture diameters.

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