Rogowskikäämit

Rogowskikäämit are flexible, air‑core coils used to measure alternating current noninvasively by surrounding a conductor. The voltage induced in the coil is proportional to the time derivative of the current flowing through the conductor, so the coil itself does not provide the actual current waveform. To obtain the current, the coil’s output must be integrated with an external integrator or measurement instrument. Because there is no magnetic core, Rogowskikäämit do not saturate and offer a wide bandwidth, making them suitable for capturing fast transients.

Construction and operation hinge on geometry. A Rogowskikäämi is typically a flat or round, insulated conductor wound into a coil around the target conductor, or wrapped around it in one or more passes. It is designed to encircle the conductor(s) with minimal gap and without closing a magnetic circuit. The transfer constant, determined by turns, size, and spacing, sets the relation between the coil voltage and the current derivative.

Applications and limitations. Rogowskikäämit are widely used in power electronics, switchgear, high-current laboratories, and pulsed-current measurements where non-contact, high‑current, and high‑bandwidth sensing are advantageous. They cannot measure direct current and require proper integration to reconstruct the current waveform. Accuracy depends on precise calibration, coil geometry, and correct placement; they are sensitive to external magnetic fields and may require multiple coils or compensation for multi-conductor setups.

History. The Rogowski coil was developed by Walter Rogowski in the early 20th century and is named in his honor; it has since become a standard tool for noninvasive current measurement in demanding applications.