Research on high current nonlinear error characteristics of fiber optic current sensor

A model for calculating the scalar factor in an interferometric digital closed-loop fiber optic current sensor is derived when the fiber retarder and the sensing fiber are working in non-ideal conditions. The key parameters leading to high current nonlinear errors in fiber optic current sensors are proposed: the alignment angle of the retarder, the phase delay angle of the retarder, and the linear birefringence of sensing fiber. The nonlinear error model of the fiber optic current sensor in the measurement range of 1~1400kA under typical parameters is simulated. A fiber-optic DC high current sensor calibration system was built, and the test results showed that the ambient nonlinear error of the sensor in the range of 16~840kA was 1.2% when the alignment angle of the retarder was 45° and the phase delay angle of the retarder was 98°, which was consistent with the theoretical derivation. The measurement error of the sensor is reduced from 1.2% to 0.15% by compensating for the nonlinear error through 3rd -order polynomial fitting modeling.