An optical current comparator for absolute current measurement

The design and performance of an optical current comparator based upon a triangular-shaped bulk glass sensing element are presented. The effect of the Faraday rotation produced in the sensing element by an unknown large current is nulled by a smaller known current of opposite polarity, thus giving an absolute measurement of the unknown current. The design requirements of the sensor configuration are analysed theoretically by computer simulation and tested experimentally for both ideal and non-ideal sensors. The sensor may have many applications in the power distribution industry, as both absolute and differential a.c. and d.c. measurements up to very high currents are possible.