Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
2000-02-14
2001-10-02
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S244100
Reexamination Certificate
active
06297625
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and to a device for measuring a magnetic field
The invention relates to a method for measuring a magnetic field as claimed in the preamble of claim
1
and to a means for carrying out the method.
German patent application No. 19545759 proposes a method for measuring a magnetic field and a means for carrying out this method. In particular, the proposed method and the proposed means serve for the measuring of a magnetic alternating field, particularly a magnetic alternating field in the environment of an electrical conductor that is passed by an alternating current.
Since the strength of the alternating current flowing though the conductor can be deduced from the strength of the alternating field measured in the environment of the conductor, when so applied the proposed method and the proposed means can be seen as a means and method for measuring current.
The optical sensing means exhibiting the Faraday effect consists of a body which is arranged in the magnetic field and which consists of a material that is transparent to light and that exhibits the Faraday effect, through which polarized light is delivered, it being possible to deduce the strength of the magnetic field from the magnitude of a torsion of the polarization planes in the passing of the light through the body.
When applied for purposes of current measurement, the transparent body of the sensing means surrounds the electrical conductor, and the polarized light is conducted in the body, accordingly.
The light is fed to the body of the sensing means on an optical path that can comprise one or more optical fibers in addition to fiber couplers for coupling the fibers with one another or for coupling a fiber with a detection means.
Vibrations occurring in the light path, for instance in a fiber, can cause undesirable disturbances in the measuring signal.
SUMMARY OF THE INVENTION
In accordance with the present invention, in a method and a device operating according to the method, a vibration compensation is achieved by conducting light through a magneto-optical sensing device in an opposite direction, thus cutting out the influence of vibrations in the measuring signal.
In any case, there are transmitted and reflected light portions. The transmitted light portions contain the measuring signal; the reflected light portions originate from jumps in the refractive index in the optical paths and act to further interfere.
If as in the present inventive method and in the present inventive device, two light sources are used instead of one, then the optical path on which the optical signal passes through the sensing means in one direction can be separated from the optical path on which the light signal passes through the sensing means in the opposite direction. This has been achieved previously by Miller, ABB, and also Sundstrom in that two light sources in the form of LEDs which generate the two optical signals are cycled in alternation, so that the back-reflected portions are shut out of the other optical path completely.
One problem with this is the relatively high clock frequency, which must lie significantly above the bandwidth of the relevant means. Given the required modulation frequencies of some tens of KHz, the emitted optical signal no longer follows the modulated rectangular shape precisely, but rather exhibits distortions—the edge steepness drops, overshoots can occur—which compromise the accuracy of the measurement.
In an embodiment, two light sources and opposing light conduction are used, thereby having the advantage that the influence of the light portions reflected on the optical path can be minimized without a push-pull modulation.
In an embodiment, in a method for measuring a magnetic field, said method comprising the steps of: transmitting a first light signal having a first polarization and a first wavelength through an optical sensor in a first direction, said optical sensor exhibiting a Faraday effect and being arranged in a region of said magnetic field; passing said transmitted first light signal through a first analyzer set to a second polarization; sending said passed first light signal to a first optical detector for detecting said first light signal, said first optical detector responding only to said first wavelength and at least not significantly to a second wavelength; generating a first intensity signal corresponding to a light intensity of said detected first light signal; transmitting a second light signal having a third polarization and said second wavelength different from said first wavelength through said optical sensor in a second direction opposite said first direction; passing said transmitted second light signal through a second analyzer set to a fourth polarization; sending said passed second light signal to a second optical detector for detecting said second light signal, said second optical detector responding only to said second wavelength; generating a second intensity signal corresponding to a light intensity of said detected second light signal; and deriving a measuring signal containing information about said magnetic field from said first intensity signal and said second intensity signal.
This advantage is inventively achieved in that, instead of the push-pull modulation or the time division multiple access method, a frequency division multiple access method is used for the two light sources; that is, the two light sources emit on different wavelengths. If a wavelength-dependent pass filter is placed in front of each detector, the two signal paths can be separated form one another entirely.
In an embodiment, the detectors and the filter are integrated with each other. Semiconductor sources are typically used as light sources, and semiconductor detectors are typically used as detectors. Based on the band spacing, the semiconductor light sources and detectors comprise a natural filtering characteristic. If the semiconductor light sources and detectors are chosen skillfully, one semiconductor detector can detect essentially only the light of one of the two semiconductor light sources, and the other semiconductor detector can detect essentially only the light of the other semiconductor light source.
Semiconductors in the form of Si and InGaP PIN diodes are cited here as examples. If a laser diode that emits at a wavelength of 670 nm is selected for one light source, then its signal can be received only by the Si diode, while the signal of a second light source, which emits at a wavelength of 1300 nm, can be received only by the InGaP diode. In this way, a high separation of optical paths or channels can be achieved in an economical manner without disturbing back-reflection or modulation.
To make the measuring signal independent of intensity fluctuations of the light signals emitted by the two light sources, the intensity of each of these light signals must be determined by means of a respective reference photoreceiver and incorporated into the signal evaluation.
The object of the present invention is also achieved in a device for measuring a magnetic field, the device comprising: an optical sensor exhibiting the Faraday effect and being arranged in a region of a magnetic field, said optical sensor having a first gate and a second gate for coupling light into said optical sensor and for coupling out light that has been coupled into said optical sensor through an other of said first gate and second gate and that has passed through said optical sensor; a first light source for generating a first light signal at a first wavelength; a second light source for generating a second light signal at a second wavelength; a first optical path leading from said first light source to one of said first gate and second gate for transmitting said first light signal to said first gate and said second gate; a second optical path leading from said second light source to an other of said first gate and said second gate than said first optical path for transmitting said second light signal to said other of said first gate and said seco
Bosselmann Thomas
Hain Stefan
Willsch Michael
Karlsen Ernest
Kobert Russell M.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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