Provided is a current measuring device such that it is possible to reliably keep the fluctuation range for the ratio error in output to within a range of ±0.5% and such that assembly thereof can be simplified. The current measuring device is configured to include at least a light entrance and exit, an optical fiber for a sensor, a Faraday rotator, a first 1/4 wavelength plate, a second 1/4 wavelength plate, a polarization separator, a light source, and a signal processing circuit comprising a photoelectric conversion element. The optical fiber for a sensor has birefringence and comprises one end into which two circularly polarized light beams having different directions of rotation enter and another end that reflects the circularly polarized light beams that have entered. In addition, the phase difference of two linearly polarized light beams in the round-trip light path between the two 1/4 wavelength plates is compensated, and the Faraday rotational angle when the Faraday rotator is magnetically saturated is set to 22.5°+a° so that the fluctuation range for the ratio error in the measured value of the current to be measured is set to be in the range of ±0.5%. In addition, the crystal axes on the optical faces of the two 1/4 wavelength plates are set to be perpendicular or are set to be in the same direction.
G01R 15/24 - Adaptations fournissant une isolation en tension ou en courant, p.ex. adaptations pour les réseaux à haute tension ou à courant fort utilisant des dispositifs modulateurs de lumière
Provided is an electric current measuring instrument wherein compensation for the ratio error versus temperature characteristics of optical fibers and Faraday rotators for a sensor can be made by an optical system of an electric current instrument and wherein the fluctuation range of ratio errors in outputs can be brought within a range of ~0. 5%. The fluctuation range of ratio errors in measured values of electric currents outputted by a signal processing circuit is set within a range of ~0. 5% over a temperature range of -20°C or more to 80°C or less by means of the following: An electric measuring instrument is constructed in such a way as to include a signal processing circuit equipped with at least a polarized light separating unit, Faraday rotators, a light source, a photoelectric conversion element, and optical fibers for a sensor. The optical fibers for the sensor are placed around the periphery of an electrical conductor through which electric current to be measured flows. Furthermore, the rotation angle of each Faraday rotator at the time when the magnetism of each Faraday rotator is saturated is set to 22.5° + .alpha.° at a temperature of 23°C, thereby changing the rotation angle of each Faraday rotator by .alpha.° from 22.5°.
G01R 15/24 - Adaptations fournissant une isolation en tension ou en courant, p.ex. adaptations pour les réseaux à haute tension ou à courant fort utilisant des dispositifs modulateurs de lumière
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