Optical electric-power sensor using one Bi₄Ge₃O₁₂ crystal

An optical electric-power sensor is proposed and experimentally carried out. Only one block of bismuth germanate crystal is utilized as the sensing element, which exhibits both the Faraday effect and the Pockels effect. The polarized light passing through the crystal can be modulated by the product signal of applied electric and magnetic fields, therefore, instantaneous electric power signal can be obtained when load current and load voltage are simultaneously applied to the sensing crystal by use of an air-cored coil and two plane electrodes. The active power and apparent power within 2000W(or VA) have been measured simultaneously under different power factors. The maximum relative errors are 2.7% for active power measurement and 1.9% for apparent power measurement. The sensitivity and uncertainty of the sensing system are also discussed.