The MOCT measures the electric current by means of Faraday Effect, which was first observed by Michael Faraday 150 years ago. The Faraday Effect is the phenomenon that the orientation of polarized light rotates under the influence of the magnetic fields and the rotation angle is proportional to the strength of the magnetic field component in the direction of optical path.
The MOCT measures the rotation angle caused by the magnetic field and converts it into a signal of few volts proportional to the electric currant. It consist of a sensor head located near the current carrying conductor, an electronic signal processing unit and fiber optical cables linking to these two parts. The sensor head consist of only optical component such as fiber optical cables, lenses, polarizers, glass prisms, mirrors etc. the signal is brought down by fiber optical cables to the signal processing unit and there is no need to use the metallic wires to transfer the signal. Therefore the insulation structure of an MOCT is simpler than that of a conventional current transformer, and there is no risk of fire or explosion by the MOCT. In addition to the insulation benefits, a MOCT is able to provide high immunity to electromagnetic interferences, wider frequency response, large dynamic range and low outputs which are compatible with the inputs of analog to digital converters. They are ideal for the interference between power systems and computer systems. And there is a growing interest in using MOCTs to measure the electric currents.