Optical current measuring systems are one way of measuring electric current touchlessly and contactlessly. They use light to determine current precisely. The advantage is that optical transformers are compact, saturation-free, linear, and high-precision. They can detect very large and very small currents in a broad frequency range.

TU Dortmund University has developed a new measurement procedure that can be used for both direct and alternating current. It consists of two radiation and fiber optic cable systems with the light of one fiber optic cable, the one surrounding the cable conducting the current, receiving a phase shift (Faraday effect) from the cable’s magnetic field. One part of the light from the first beam splitter is conducted to the second beam splitter, from which the light beam is sent on to the quarter-wave plate. The two resulting light beams move through a collimator and an in-line calcite double breaker to photodiodes. An evaluation circuit thus allows electrical current in the current-carrying cable to be determined optically. The system functions in a temperature-compensated manner.