The FS205 is a high precision DC high current measurement device based on the Faraday Magneto-optical Effect and the Ampere Loop Theorem. The sensing optical fiber is fixedly mounted on the high current busbar through a skeleton and forms a closed optical fiber loop. The magnetic field generated by the high current in the busbar causes the phase shift of two light waves in the optical fiber, and the current value is measured by demodulating the phase shift of the light waves.