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LEM has introduced of the first AC current sensors range of components based on Perfect Loop Technology.

After calibration, the RT series achieves absolute accuracy of better than 0.65 per cent – including the position error – making them the first split-core Rogowski coils to be suitable for use in Class 1 power devices.

An imperfect coil structure induces an unbalanced geometry and increases sensitivity to the position of the measured conductor within the sensor, or to the proximity of external electric cables.

LEM engineers have invented a magnetic coupling technology that allows a perfect extension of the magnetic flux at the loop opening that compensates for coil asymmetry.

LEM has also developed a coil-winding process that produces regular windings to enhance sensor symmetry, accuracy and immunity to electromagnetic interference.

Sensors based on conventional Rogowski coil technology combine almost perfect linearity, with no saturation or upper limit in the current rating, a large frequency range which includes 50/60Hz, and an ultra-compact and flexible form.

LEM said that its RT sensors retain these benefits while overcoming susceptibility to asymmetry caused by discontinuity at the sensor opening and minimising unevenness in the coil winding.

The Rogowski coil principle provides precise detection of the rate of change (derivative) of the primary current that induces a proportionate voltage at the terminals of the coil.

An electronic integrator circuit is used to convert the voltage signal into an output signal that is proportional to the primary current.

This eliminates the need for an additional power supply as the RT sensor is self-powered.

The thin, light and flexible format of RT sensors allows them to be fitted into applications in which traditional current transformers are typically too heavy and bulky, especially when measuring high currents.

Their split-core construction allows them to be easily wrapped around the conductor without dismantling cables or shutting down operation.

The 5mm gauge RT sensors are available with sensing apertures with diameters of 55 or 125mm and have a five-year guarantee.

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