Tuesday, October 09, 2012

LEM sets new benchmark for accuracy in Rogowski coil sensors

LEM announces the introduction of the first AC current sensors family of components based on patent-pending Perfect Loop Technology. After calibration, the new RT series achieves absolute accuracy of better than 0.65% - 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. The RT series of sensors overcomes the problem of asymmetry resulting from the discontinuity at the sensor opening, which is inherent in conventional split-core Rogowski coils. Whilst other manufacturers use complex and costly clasp designs to minimise the effects of discontinuity, LEM engineers have invented a unique, patent-pending magnetic coupling technology that allows a perfect extension of the magnetic flux at the loop opening which compensates for coil asymmetry.

In addition, LEM has developed an advanced coil-winding process which produces exceptionally regular windings, to further 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 50/60 Hz, and an ultra-compact and flexible form. LEM’s RT sensors retain these key benefits whilst overcoming susceptibility to asymmetry caused by discontinuity at the sensor opening, and minimizing unevenness in the coil winding.

The Rogowski coil principle provides very precise detection of the rate of change (derivative) of the primary current that induces a proportionate voltage at the terminals of the coil. A simple electronic integrator circuit, typically within the device to which the sensor is connected, 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 very 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 benchmark accuracy of RT series sensors provides enhanced performance in current and power monitors as well as energy meters.

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

No comments: