Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-04-04
1999-04-20
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
324 96, 3242441, G01R 33032
Patent
active
058959122
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND INFORMATION
The present invention relates to a method and a device for measuring an alternating electric quantity. In this case, an alternating electric quantity is understood to be an electric quantity which varies with time and whose frequency spectrum lies above a predetermined frequency. In particular, the alternating quantity can be an alternating electric current, an alternating electric voltage, or even an alternating electric field.
Optical measuring methods and measuring devices for measuring electric quantities such as current, voltage, or field are known, in which the change in polarization of polarized measuring light in a sensor device as a function of the electric quantity is evaluated. In this case, the magneto-optical Faraday effect is used for measuring an electric quantity; for measuring electric voltages and fields, on the other hand, the electro-optical Pockels effect is used.
The Faraday effect is understood to be the rotation of the plane of polarization of linearly polarized light as a function of a magnetic field. The angle of rotation is, in this case, proportional to the path integral over the magnetic field along the path traced by the light, with the Verdet constants as constants of proportionality. The Verdet constant depends on the material in which the light runs and on the wavelength of the light. To measure an electric current in a current conductor using the Faraday effect, a Faraday element, which consists of an optically transparent material, such as glass, is arranged as a sensor device in the vicinity of the current conductor. Linearly polarized light is sent through the Faraday element. The magnetic field generated by the electric current effects a rotation of the plane of polarization of the light in the Faraday element around an angle of rotation. The angle of rotation can be evaluated by an evaluation unit as a measure of the intensity of the magnetic field and thus of the strength of the electric current. In general, the Faraday element surrounds the current conductor, so that the polarized light circulates around the current conductor in a quasi-closed path. In this case, the amount of the angle of rotation of the polarization is, to a good approximation, directly proportional to the amplitude of the measured current.
WO 91/01501 discloses an optical measuring device for measuring an electric current, having a Faraday element which is designed as part of an optical monomode fiber. The Faraday element surrounds the current conductor in the form of a measuring winding.
EP-B-0 088 419 discloses an optical measuring device for measuring a current, in which the Faraday element is designed as a solid glass ring around the current conductor.
The electro-optical Pockels effect is understood to be the change in the polarization of polarized measuring light in a material exhibiting the Pockels effect as a result of a linear birefringence that is induced in the material. On the basis of the electro-optical coefficients, the pockels effect is essentially linearly dependent on an electric field penetrating the material. To measure an electric field, a Pockels element made of a material showing the Pockels effect is arranged in the electric field as a sensor device. To measure an electric voltage, the voltage to be measured is applied to two electrodes assigned to the Pockels element and the corresponding, adjacent, electric field is measured. Polarized measuring light is transmitted through the Pockels element, and the change in polarization of the polarized measuring light as a function of the voltage to be measured or of the field to be measured is evaluated with the aid of a polarization analyzer.
In order to measure a current using a Faraday element and a voltage using a Pockels element, a polarizing beam splitter or a simple beam splitter with two polarizers arranged downstream can be provided as a polarization analyzer (EP-B-0 088 419 and DE-C-34 04 608). The polarizing beam splitter may comprise a Wollaston prism. The polarized measuring light which has pas
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Bosselmann Thomas
Menke Peter
Luu Thanh X.
Siemens Aktiengesellschaft
Westin Edward P.
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