Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
2001-06-21
2003-02-04
Gutierrez, Diego (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S11700H, C324S244100, C250S227170, C250S225000, C250S227190, C356S368000
Reexamination Certificate
active
06515467
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to a system and method for optically detecting for optically detecting an electric current, and in particular, to optically detecting an electric current by using light signals having different wavelengths.
BACKGROUND OF THE INVENTION
WO 98/38517 A1 describes an arrangement for measuring current, in which two light signals each having a different wavelength are generated and are fed via a coupler into an optical waveguide. The optical waveguide serves as a common feed to a Faraday element. Before entering the Faraday element, both light signals are linearly polarized. In this connection, linear polarization is to be regarded as a particularly favorable special form of elliptical polarization. Generally, however, any other elliptical polarization form is equally suitable as long as it has a marked direction. The first light signal has a wavelength of between 630 and 850 nm and the second light signal has a wavelength of between 1300 and 1550 nm. On account of the wavelength-dependent Verdet's constant, the polarizations of the two light signals arc influenced to different extents in the Faraday element. The changes in polarization caused by the current are evaluated in a single-channel or two-channel manner. In an evaluation unit; the two light signals are separated from one another in accordance with their wavelength by means of optical filter elements or by means of the sensitivity range of the photodiodes used and are converted into electrical signals for further processing. In this case, the wavelength difference between the two light signals has the effect that the electrical signal derived from the first light signal is an unambiguous function of the current to be measured and the electrical signal derived from the other light signal is a non-unambiguous, periodic function of the current to be measured. By the same token, however, the second derived electrical signal has a higher measurement resolution. From these two electrical signals, a measurement quantity for the electric current is derived with a large measurement range and also with a high measurement resolution. The method used in this case is disclosed in DE 195 44 778 A1.
DE 195 44 778 A1 describes a magneto-optical current converter having two Faraday elements for deriving two different measurement signals. The first Faraday element yields a first measurement signal which, in a predetermined measurement range, is an unambiguous function of the electric current to be measured (=operation in the unambiguity range). By contrast, the second Faraday element is configured in such a way that a second measurement signal that it generates is a non-unambiguous, essentially periodic function of the electric current (=operation in the ambiguity range). A third measurement signal for the electric current is built up from the two measurement signals. The third measurement signal is in the predetermined measurement range. Both signals are an unambiguous function of the measurement quantity and have the same high measurement resolution as the second measurement signal. However, the method described requires a relatively high outlay since two separate Faraday elements. A high computation complexity is also required in the formation of the third measurement signal in an evaluation unit.
Moreover, EP 0 210 716 A1 describes a magneto-optical current sensor which is operated with two light signals having different wavelengths. In this case the two wavelengths do not serve for extending the measurement range, but for drift compensation. The Faraday element is again operated only in the linear, i.e. unambiguous, range of the characteristic curve.
DE 31 41 325 A1 discloses a heterodyne method for optical current measurement, in which two light signals having the same wavelength but different intensity modulation are generated. The frequency difference of the intensity modulation between the two light signals is between 1 kHz and 1 MHz. From these two light signals there is generated a further light signal with a linear polarization vector which rotates with the differential frequency of the two intensity modulations about the direction of propagation of the further light signal. The light signal with rotating linear polarization vector is then both fed into a Faraday element and transmitted as reference signal directly to an evaluation unit. The electric current is then determined by phase comparison between the reference signal and the light signal emerging from the Faraday element. This method also makes it possible to extend the measurement range for the optical current measurement beyond the unambiguity range. However, this method is relatively complex owing to the reference signal and the phase-comparison measuring devices required in the evaluation unit.
WO 98/05975 A1 describes a method and an arrangement for optical current detection, in which two optical measurement signals are generated as a function of the electric current to be measured. The dependence of the two optical measurement signals on the electric current is in each case periodic, the two periods differing from one another at most by the factor 2. From the two optical measurement signals there are derived value pairs to which it is then possible to assign in each case a present value of the electric current to be measured. The procedure described by this method likewise makes it possible to extend the measurement range in the case of optical current detection. However, WO 98/05975 A1 contains no embodiments which are distinguished, for example by particular efficiency.
SUMMARY OF THE INVENTION
In one embodiment of the invention, there is an electric current generates at least one first elliptically polarized light signal having a first polarization and a first wavelength and a second elliptically polarized light signal having a second polarization and a second wavelength, which is different from the first wavelength. The electric current feeds the first and the second light signal into a Faraday element, changes the first and the second polarization as a function of the electric current upon passage through the Faraday element, and derives a measurement signal for the electric current from the changes in polarization of the two light signals. The first and the second polarization are rotated by at least 0.0014° per ampere of the electric current, and at least one of the two polarizations is rotated by more than 45° under the influence of a maximum electric current.
In one aspect of the invention, the first and the second polarization are rotated in the Faraday element by a first and a second angle of rotation. The first and the second angle of rotation differ at most by a factor 2 given at a predetermined electric current.
In another aspect of the invention, there is a wavelength difference between the first and the second wavelength of at most 15% of an average value of the first and second wavelengths. In another aspect of the invention, the first and the second light signals pass through the Faraday element simultaneously.
In yet another aspect of the invention, the first and the second light signals pass through the Faraday element cyclically alternately.
In a further aspect of the invention, the first and the second light signal are generated from an optical swept-frequency signal having a varying wavelength. The varying wavelength is tuned between the first wavelength and the second wavelength.
In a further aspect of the invention, the varying wavelength of the optical swept-frequency signal is tuned periodically between the first wavelength and the second wavelength.
In yet another aspect of the invention, the first and the second light signal are intensity-modulated during generation with a first and a second frequency.
In another embodiment of the invention, a transmitting device generates at least one first elliptically polarized light signal having a first polarization and a first wavelength and a second elliptically polarized light signal having a second polarization and a secon
Bosselmann Thomas
Mohr Stephan
Willsch Michael
Hamdan Wasseem H.
Morrison & Foerster / LLP
Siemens Aktiengesellschaft
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