Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Analysis of complex waves
Reexamination Certificate
2001-02-22
2003-10-07
Lefkowitz, Edward (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Analysis of complex waves
C324S537000, C324S096000, C324S076110, C324S244100
Reexamination Certificate
active
06630819
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to current sensors which do not require a direct electrical circuitry connection to the conductor in the circuit whose current is being sensed. Particularly, the invention relates to current sensors of the type utilizing the Faraday effect. More particularly still, the invention relates to current sensors utilizing thin-film magneto-optic sensing elements.
BACKGROUND OF THE INVENTION
Current measuring devices and magnetometers have been developed, all based upon the Faraday effect. The Faraday effect causes the plane of polarization of a polarized beam of light passing through a transparent substance exhibiting the Faraday effect to rotate from the plane of polarization of the instant light by an amount proportional to the magnetic field passing through the substance parallel to the optical axis of the beam of light.
High-power electronics will be a multi-billion dollar market in the next decade encompassing industries as diverse as power utilities, automotive manufacturing, and navel ship construction. A crucial component in the emerging circuit designs for DC/AC inverters and DC/DC converters is the precise monitoring of high currents (typically up to the range of 300 amps to 500 amps). The current sensors to be used in these designs must fulfill several stringent requirements including, but not limited to: (a) operation over a wide frequency range (DC to 10 MHz) for the precise monitoring of pulse trains; (b) operation at elevated temperatures up to 150 degrees C. without the necessity of additional temperature sensors; (c) operation in the presence of large electromotive force (EMF) and mechanical vibrations; and (d) total electrical isolation in order to avoid any possibility of shorts between high power and control circuits. These requirements are difficult to satisfy with sensors that are based on traditional technology such as Hall effect, magneto resistance, pick-up coils, and shunt resistors. In particular, requirement (d) rules out any “electric” type sensor. Presently, at least one optical current sensor is commercially available, however, it requires wrapping long lengths of optical fiber around the current carrying conductor.
Accordingly, there is a need and desire for current sensors based on the Faraday effect. Also, there is a need and desire for sensors utilizing magneto-optic sensor material. Further still, there is a need and desire for magneto-optic current sensors that are able to operate over a wide frequency range. Yet further still, there is a need for magneto-optic sensors that are capable of operating at elevated temperatures. Yet further still, there is a need and desire for magneto-optic sensors that may operate in the presence of large EMF and mechanical vibrations. Yet further still, there is a need and desire for magneto-optic sensors that are electrically isolated from the circuit in which they are sensing current.
SUMMARY OF THE INVENTION
An exemplary embodiment of the invention relates to an optical current transducer configured to sense current in a conductor. The optical current transducer includes a light source and a polarizer configured to generate linearly polarized light received from the light source. The optical current transducer also includes a magneto-optic garnet comprising bismuth (Bi), iron (Fe), and oxygen (0). The magneto-optic garnet is configured to be coupled to the conductor and is in optical communication with the polarizer. The magneto-optic garnet is configured to rotate the polarization of the linearly polarized light received from the polarizer. Further, the optical current transducer includes an analyzer in optical communication with the magneto-optic garnet, the analyzer is configured to detect the rotation of the linearly polarized light caused by the magneto-optic garnet.
Another exemplary embodiment of the invention relates to a method of measuring current in a conductor. The method includes providing a light source and communicating light from the light source to a polarizer that is configured to generate linearly polarized light. The method also includes communicating the linearly polarized light from the polarizer to a magneto-optic garnet comprising bismuth (Bi), iron (Fe), and oxygen (O). The magneto-optic garnet is configured adjacent the conductor so that the magnetic field vector, caused by the conductor current, is perpendicular to the garnet file surface. The magneto-optic garnet is configured to rotate the polarization of the linearly polarized light received from a polarizer. Further, the method includes communicating the rotated light from the magneto-optic garnet to an analyzer in optical communication with the magneto-optic garnet. The analyzer is configured to detect the rotation of the linearly polarized light caused by the magneto-optic garnet.
Further, an exemplary embodiment of the invention relates to an optical current transducer configured to sense current in a conductor. The optical current transducer includes a light source and a sensor head. The sensor head includes a polarizer configured to generate linearly polarized light received from the light source. The sensor head also includes a magneto-optic garnet comprising bismuth (Bi), iron (Fe), and oxygen (O). The magneto-optic garnet is configured to be coupled to the conductor and is in optical communication with the polarizer. The magneto-optic garnet is configured to rotate the polarization of the linearly polarized light received from the polarizer. The sensor head further includes an analyzer in optical communication with the magneto-optic garnet. The analyzer is configured to detect the rotation of the linearly polarized light caused by the magneto-optic garnet.
Further still, an exemplary embodiment of the invention relates to a method of temperature compensation for a current sensor. The method includes providing a light source including more than one wavelength to a sensor head. The method also includes measuring the light intensity of more than one wavelength of light. Further, the method includes determining the temperature of the current sensor based on at least one ratio of light intensity of one wavelength of light to another wavelength of light. Further still, the method includes determining a Verdet Constant based on the temperature, determining light intensity based on the temperature and the Verdet Constant, and determining the current detected by the current sensor based on the temperature and Verdet Constant.
Yet further still, an exemplary embodiment of the invention relates to a method of determining the temperature of a current sensor. The method includes providing a light source having a first wavelength and a second wavelength. The method also includes providing a current sensor head for receiving light from the light source. Further, the method includes detecting light intensity at the first wavelength and at the second wavelength from the current sensor head. Further still, the method includes determining temperature of the sensor head based on a ratio of light intensity of the first wavelength to light intensity of the second wavelength.
Yet further still, an exemplary embodiment relates to a method of determining sensor drift for a current sensor. The method includes providing a light source having a first wavelength, a second wavelength, and a third wavelength. The method also includes providing a current sensor head for receiving light from the light source. Further, the method includes detecting light intensity at the first wavelength, at the second wavelength, and at the third wavelength, the light coming from the sensor head. Further still, the method includes determining a first intensity ratio of the first intensity and third intensity and a second intensity ratio of the second intensity and the third intensity. Yet further still, the method includes determining sensor drift over time based on the first intensity ratio and the second intensity ratio.
REFERENCES:
patent: 3980949 (1976-09-01), Feldtkeller
patent: 4604577 (1986-08-01), Matsumura et al.
pate
Fisher Brandon L.
Lanagan Michael T.
Valsko-Vlasov Vitalii K.
Welp Ulrich
Foley & Lardner
Lefkowitz Edward
Sundaram T. R.
The University of Chicago
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