Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Patent
1996-04-01
1998-09-22
Karlsen, Ernest F.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
324117R, G01R 33032, G01R 1524
Patent
active
058119647
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE94/01104 filed Sep. 22, 1994.
FIELD OF THE INVENTION
The present invention relates to a method and a device for measuring an electrical alternating quantity. In this case, an electrical alternating quantity is understood to include an electrical alternating current, an electrical alternating voltage or an electrical alternating field.
BACKGROUND INFORMATION
Optical measuring methods and measuring devices are used for measuring electrical quantities such as current, voltage or field are known, in which the change in polarization of polarized measuring light as a function of the electrical quantity is evaluated. The magneto-optical Faraday effect is used for measuring an electrical current, and the electro-optical Pockels effect for measuring electrical voltages and fields.
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 constant as a constant of proportionality. The Verdet constant depends on the material in which the light travels and on the wavelength of the light. For measuring an electrical current in a current conductor, using the Faraday effect, a Faraday element, which consists of an optically transparent material and generally of glass, is arranged in the vicinity of the current conductor. Linearly polarized light is sent through the Faraday element. The magnetic field generated by the electrical current effects a rotation of the plane of polarization of the light in the Faraday element through an angle of rotation which can be evaluated by an evaluation unit as a measure of the intensity of the magnetic field and, thus, of the intensity of the electrical 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.
In one embodiment of an optical measuring device for measuring an electrical current, disclosed in WO 91/01501, the Faraday element is designed as a part of an optical monomode fiber, which surrounds the current conductor in the form of a measuring winding. The polarized measuring light, therefore, circulates around the current conductor N times in one pass, if N is the number of turns of the measuring winding. In the so-called transmission type, the measuring light passes through the measuring winding only once. In the reflection type, on the other hand, the other end of the fiber is silvered, so that the measuring light, after a first pass, passes through the measuring winding a second time in the reverse direction. Because of the non-reciprocity of the Faraday effect, the angle of rotation in the reflection type is, therefore, twice as large in the same measuring winding as in the transmission type.
The reference 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. Light from a light source is linearly polarized with a polarizer and is then coupled into the Faraday element. The linearly polarized light passes through the Faraday element once and is then split, using a Wollaston prism as a polarizing beam-splitter, into two linearly polarized partial light signals A and B having planes of polarization directed perpendicularly to each other. Each of these two light signals A and B is transmitted via an associated optical transmission fiber to an associated light detector and converted into a corresponding electrical signal PA and PB. An intensity-normalized measured signal measured signal M is independent of intensity fluctuations of the light source or attenuations in the optical feed lines.
By the electro-optical Pockels effec
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Ulmer, Jr., High Accuracy Faraday Rotation Measurements, Proc. Conf. Opt. Fiber Sensor, 1988, pp. 288-291, (month unavailable).
Bosselmann Thomas
Menke Peter
Niewisch Joachim
Karlsen Ernest F.
Siemens Aktiengelsellschaft
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